diff --git a/src-tauri/Cargo.lock b/src-tauri/Cargo.lock
index 39287d6..4dc1269 100644
--- a/src-tauri/Cargo.lock
+++ b/src-tauri/Cargo.lock
@@ -4236,10 +4236,12 @@ version = "0.1.0"
 dependencies = [
  "base64 0.22.1",
  "chrono",
+ "percent-encoding",
  "rusqlite",
  "rusqlite_migration",
  "serde",
  "serde_json",
+ "sha2",
  "tauri",
  "tauri-build",
  "tauri-plugin-dialog",
diff --git a/src-tauri/Cargo.toml b/src-tauri/Cargo.toml
index 8ead673..17a2e79 100644
--- a/src-tauri/Cargo.toml
+++ b/src-tauri/Cargo.toml
@@ -26,6 +26,8 @@ chrono = { version = "0.4", features = ["serde"] }
 uuid = { version = "1", features = ["v4"] }
 thiserror = "2"
 base64 = "0.22"
+sha2 = "0.10"
+percent-encoding = "2"
 
 # Desktop-only plugins (not available on mobile targets).
 [target.'cfg(not(any(target_os = "android", target_os = "ios")))'.dependencies]
diff --git a/src-tauri/src/commands/archive.rs b/src-tauri/src/commands/archive.rs
new file mode 100644
index 0000000..5ef4e75
--- /dev/null
+++ b/src-tauri/src/commands/archive.rs
@@ -0,0 +1,289 @@
+//! Content-addressed archive of the searchable PDF produced when an invoice is issued.
+//! Files live at `<local data dir>/archive/<sha256>.pdf`; the invoice row keeps the hash.
+use super::raw::{header_map, raw_body, required_header, write_atomic, Headers};
+use crate::AppState;
+use rusqlite::{params, Connection, OptionalExtension};
+use serde::Serialize;
+use sha2::{Digest, Sha256};
+use std::path::{Path, PathBuf};
+use tauri::ipc::{Request, Response};
+use tauri::State;
+
+pub const MAX_ARCHIVE_BYTES: usize = 64 * 1024 * 1024;
+const MAX_FINGERPRINT_LEN: usize = 256;
+
+#[derive(Debug, Clone, Serialize, PartialEq, Eq)]
+#[serde(rename_all = "camelCase")]
+pub struct ArchiveStatus {
+    pub archived: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub sha256: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub fingerprint: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub archived_at: Option<String>,
+}
+
+fn sha256_hex(bytes: &[u8]) -> String {
+    format!("{:x}", Sha256::digest(bytes))
+}
+
+/// The hash comes from the database, but it ends up in a file path, so check its shape.
+fn archive_path(local_dir: &Path, sha256: &str) -> Result<PathBuf, String> {
+    let valid = sha256.len() == 64 && sha256.bytes().all(|b| matches!(b, b'0'..=b'9' | b'a'..=b'f'));
+    if !valid {
+        return Err("The stored archive hash is malformed".to_string());
+    }
+    Ok(local_dir.join("archive").join(format!("{sha256}.pdf")))
+}
+
+fn parse_invoice_id(headers: &Headers) -> Result<i64, String> {
+    required_header(headers, "x-invoice-id")?
+        .trim()
+        .parse::<i64>()
+        .map_err(|_| "x-invoice-id must be a number".to_string())
+}
+
+pub fn archive_pdf_impl(
+    conn: &mut Connection,
+    local_dir: &Path,
+    bytes: &[u8],
+    headers: &Headers,
+) -> Result<String, String> {
+    let id = parse_invoice_id(headers)?;
+    let fingerprint = required_header(headers, "x-fingerprint")?.trim();
+    if fingerprint.is_empty() || fingerprint.len() > MAX_FINGERPRINT_LEN {
+        return Err("x-fingerprint must be 1-256 characters".to_string());
+    }
+    if !bytes.starts_with(b"%PDF-") {
+        return Err("The data is not a PDF".to_string());
+    }
+    if bytes.len() > MAX_ARCHIVE_BYTES {
+        return Err("The PDF is larger than the 64 MB archive limit".to_string());
+    }
+
+    let row: Option<(String, Option<String>)> = conn
+        .query_row(
+            "SELECT status, archived_pdf_sha256 FROM invoices WHERE id = ?1",
+            params![id],
+            |r| Ok((r.get(0)?, r.get(1)?)),
+        )
+        .optional()
+        .map_err(|e| e.to_string())?;
+    let (status, existing) = row.ok_or_else(|| "Invoice not found".to_string())?;
+    if status != "issued" && status != "cancelled" {
+        return Err(format!("Only an issued invoice can be archived (this one is {status})"));
+    }
+
+    let sha = sha256_hex(bytes);
+    if let Some(existing) = &existing {
+        if *existing != sha {
+            return Err(
+                "This invoice already has an archived original; the issued PDF cannot be replaced"
+                    .to_string(),
+            );
+        }
+    }
+
+    let path = archive_path(local_dir, &sha)?;
+    std::fs::create_dir_all(path.parent().expect("archive path has a parent"))
+        .map_err(|e| format!("Could not create the archive folder: {e}"))?;
+    // Same content, same name; a matching length means the file is already in place.
+    let present = std::fs::metadata(&path).map(|m| m.len() == bytes.len() as u64).unwrap_or(false);
+    if !present {
+        write_atomic(&path, bytes)?;
+    }
+
+    if existing.is_none() {
+        let now = chrono::Utc::now().to_rfc3339();
+        conn.execute(
+            "UPDATE invoices SET archived_pdf_sha256 = ?1, archived_fingerprint = ?2, archived_at = ?3
+             WHERE id = ?4",
+            params![sha, fingerprint, now, id],
+        )
+        .map_err(|e| e.to_string())?;
+    }
+    Ok(sha)
+}
+
+pub fn read_archive_impl(conn: &Connection, local_dir: &Path, id: i64) -> Result<Vec<u8>, String> {
+    let sha = stored_sha(conn, id)?.ok_or_else(|| "This invoice has no archived PDF".to_string())?;
+    let path = archive_path(local_dir, &sha)?;
+    let bytes = std::fs::read(&path).map_err(|e| {
+        if e.kind() == std::io::ErrorKind::NotFound {
+            "The archived PDF file is missing".to_string()
+        } else {
+            format!("Could not read the archived PDF: {e}")
+        }
+    })?;
+    if sha256_hex(&bytes) != sha {
+        return Err("The archived PDF is corrupted (its checksum no longer matches)".to_string());
+    }
+    Ok(bytes)
+}
+
+fn stored_sha(conn: &Connection, id: i64) -> Result<Option<String>, String> {
+    let row: Option<Option<String>> = conn
+        .query_row("SELECT archived_pdf_sha256 FROM invoices WHERE id = ?1", params![id], |r| r.get(0))
+        .optional()
+        .map_err(|e| e.to_string())?;
+    row.ok_or_else(|| "Invoice not found".to_string())
+}
+
+pub fn archive_status_impl(conn: &Connection, id: i64) -> Result<ArchiveStatus, String> {
+    let row: Option<(Option<String>, Option<String>, Option<String>)> = conn
+        .query_row(
+            "SELECT archived_pdf_sha256, archived_fingerprint, archived_at FROM invoices WHERE id = ?1",
+            params![id],
+            |r| Ok((r.get(0)?, r.get(1)?, r.get(2)?)),
+        )
+        .optional()
+        .map_err(|e| e.to_string())?;
+    let (sha256, fingerprint, archived_at) = row.ok_or_else(|| "Invoice not found".to_string())?;
+    Ok(ArchiveStatus { archived: sha256.is_some(), sha256, fingerprint, archived_at })
+}
+
+// The commands are async so hashing and file I/O of a multi-MB PDF stay off the main thread.
+#[tauri::command]
+pub async fn archive_pdf(request: Request<'_>, state: State<'_, AppState>) -> Result<String, String> {
+    let bytes = raw_body(&request)?;
+    let headers = header_map(&request);
+    let mut conn = state.db.lock().map_err(|e| e.to_string())?;
+    archive_pdf_impl(&mut conn, &state.local_data_dir, bytes, &headers)
+}
+
+#[tauri::command]
+pub async fn read_archive(invoice_id: i64, state: State<'_, AppState>) -> Result<Response, String> {
+    let conn = state.db.lock().map_err(|e| e.to_string())?;
+    read_archive_impl(&conn, &state.local_data_dir, invoice_id).map(Response::new)
+}
+
+#[tauri::command]
+pub async fn archive_status(invoice_id: i64, state: State<'_, AppState>) -> Result<ArchiveStatus, String> {
+    let conn = state.db.lock().map_err(|e| e.to_string())?;
+    archive_status_impl(&conn, invoice_id)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::tempdir;
+
+    fn conn_with_invoice(status: &str) -> Connection {
+        let conn = crate::db::open_in_memory().unwrap();
+        conn.execute(
+            "INSERT INTO invoices (number, invoice_date, client_name, status, created_at, updated_at)
+             VALUES ('AP/2026-001', '2026-04-01', 'Client', ?1, 'now', 'now')",
+            params![status],
+        )
+        .unwrap();
+        conn
+    }
+
+    fn headers(id: &str) -> Headers {
+        Headers::from([
+            ("x-invoice-id".to_string(), id.to_string()),
+            ("x-fingerprint".to_string(), "fp-1".to_string()),
+        ])
+    }
+
+    const PDF: &[u8] = b"%PDF-1.7\nbody";
+
+    #[test]
+    fn archives_once_and_is_idempotent() {
+        let dir = tempdir().unwrap();
+        let mut conn = conn_with_invoice("issued");
+        let sha = archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("1")).unwrap();
+        assert_eq!(sha.len(), 64);
+        assert_eq!(std::fs::read(dir.path().join("archive").join(format!("{sha}.pdf"))).unwrap(), PDF);
+
+        let status = archive_status_impl(&conn, 1).unwrap();
+        assert!(status.archived);
+        assert_eq!(status.sha256.as_deref(), Some(sha.as_str()));
+        assert_eq!(status.fingerprint.as_deref(), Some("fp-1"));
+        let first_at = status.archived_at.clone().unwrap();
+
+        let again = archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("1")).unwrap();
+        assert_eq!(again, sha);
+        assert_eq!(archive_status_impl(&conn, 1).unwrap().archived_at.unwrap(), first_at);
+        assert_eq!(read_archive_impl(&conn, dir.path(), 1).unwrap(), PDF);
+    }
+
+    #[test]
+    fn cancelled_invoices_can_be_archived() {
+        let dir = tempdir().unwrap();
+        let mut conn = conn_with_invoice("cancelled");
+        assert!(archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("1")).is_ok());
+    }
+
+    #[test]
+    fn different_bytes_for_an_archived_invoice_are_refused() {
+        let dir = tempdir().unwrap();
+        let mut conn = conn_with_invoice("issued");
+        let sha = archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("1")).unwrap();
+        let err = archive_pdf_impl(&mut conn, dir.path(), b"%PDF-1.7\nother", &headers("1")).unwrap_err();
+        assert!(err.contains("already has an archived original"), "{err}");
+        assert_eq!(archive_status_impl(&conn, 1).unwrap().sha256.unwrap(), sha);
+        assert_eq!(std::fs::read_dir(dir.path().join("archive")).unwrap().count(), 1);
+    }
+
+    #[test]
+    fn non_pdf_and_oversize_bodies_are_refused() {
+        let dir = tempdir().unwrap();
+        let mut conn = conn_with_invoice("issued");
+        assert!(archive_pdf_impl(&mut conn, dir.path(), b"<html>", &headers("1"))
+            .unwrap_err()
+            .contains("not a PDF"));
+        let mut big = b"%PDF-".to_vec();
+        big.resize(MAX_ARCHIVE_BYTES + 1, 0);
+        assert!(archive_pdf_impl(&mut conn, dir.path(), &big, &headers("1"))
+            .unwrap_err()
+            .contains("64 MB"));
+        assert!(!archive_status_impl(&conn, 1).unwrap().archived);
+    }
+
+    #[test]
+    fn drafts_unknown_invoices_and_bad_headers_are_refused() {
+        let dir = tempdir().unwrap();
+        let mut conn = conn_with_invoice("draft");
+        assert!(archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("1"))
+            .unwrap_err()
+            .contains("Only an issued invoice"));
+        assert_eq!(
+            archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("99")).unwrap_err(),
+            "Invoice not found"
+        );
+        assert!(archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("abc")).is_err());
+        let mut no_fp = headers("1");
+        no_fp.remove("x-fingerprint");
+        assert!(archive_pdf_impl(&mut conn, dir.path(), PDF, &no_fp).is_err());
+        assert!(!dir.path().join("archive").exists());
+    }
+
+    #[test]
+    fn read_archive_detects_corruption_and_missing_files() {
+        let dir = tempdir().unwrap();
+        let mut conn = conn_with_invoice("issued");
+        assert!(read_archive_impl(&conn, dir.path(), 1).unwrap_err().contains("no archived PDF"));
+        let sha = archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("1")).unwrap();
+        let file = dir.path().join("archive").join(format!("{sha}.pdf"));
+
+        std::fs::write(&file, b"%PDF-1.7\ntampered").unwrap();
+        assert!(read_archive_impl(&conn, dir.path(), 1).unwrap_err().contains("corrupted"));
+
+        std::fs::remove_file(&file).unwrap();
+        assert!(read_archive_impl(&conn, dir.path(), 1).unwrap_err().contains("missing"));
+        // Archiving the same bytes again restores the file.
+        archive_pdf_impl(&mut conn, dir.path(), PDF, &headers("1")).unwrap();
+        assert_eq!(read_archive_impl(&conn, dir.path(), 1).unwrap(), PDF);
+    }
+
+    #[test]
+    fn a_malformed_stored_hash_never_becomes_a_path() {
+        let dir = tempdir().unwrap();
+        let conn = conn_with_invoice("issued");
+        conn.execute("UPDATE invoices SET archived_pdf_sha256 = '../../etc/passwd' WHERE id = 1", [])
+            .unwrap();
+        assert!(read_archive_impl(&conn, dir.path(), 1).unwrap_err().contains("malformed"));
+    }
+}
diff --git a/src-tauri/src/commands/assets.rs b/src-tauri/src/commands/assets.rs
index 95290f1..009fb99 100644
--- a/src-tauri/src/commands/assets.rs
+++ b/src-tauri/src/commands/assets.rs
@@ -133,22 +133,6 @@ pub fn remove_asset(state: State<AppState>, path: String) -> Result<(), String>
     remove_asset_file(&state.data_dir, &path)
 }
 
-/// Write a base64 payload (e.g. a generated PDF) to a user-chosen path.
-#[tauri::command]
-pub fn save_binary_file(path: String, data_base64: String) -> Result<(), String> {
-    if path.trim().is_empty() {
-        return Err("No file path given".into());
-    }
-    let bytes = STANDARD
-        .decode(data_base64.as_bytes())
-        .map_err(|e| e.to_string())?;
-    if let Some(parent) = Path::new(&path).parent() {
-        // A missing parent is created; if that fails the write below reports the real error.
-        std::fs::create_dir_all(parent).ok();
-    }
-    std::fs::write(&path, bytes).map_err(|e| e.to_string())
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -248,9 +232,4 @@ mod tests {
         assert!(remove_asset_file(dir.path(), "voiced.db").is_err());
         assert!(dir.path().join("voiced.db").exists());
     }
-
-    #[test]
-    fn save_binary_file_rejects_empty_path() {
-        assert!(save_binary_file("  ".into(), "AAAA".into()).is_err());
-    }
 }
diff --git a/src-tauri/src/commands/files.rs b/src-tauri/src/commands/files.rs
new file mode 100644
index 0000000..39bb9e6
--- /dev/null
+++ b/src-tauri/src/commands/files.rs
@@ -0,0 +1,211 @@
+//! User-visible files: exports written to a path from the save dialog, and the
+//! reveal/open helpers used afterwards.
+use super::raw::{decode_header_path, header_map, raw_body, required_header, write_atomic, Headers};
+use crate::AppState;
+use rusqlite::{params, Connection};
+use std::path::{Path, PathBuf};
+use std::process::Command;
+use tauri::ipc::Request;
+use tauri::State;
+use tauri_plugin_opener::OpenerExt;
+
+pub fn write_export_file_impl(
+    conn: &Connection,
+    bytes: &[u8],
+    headers: &Headers,
+) -> Result<String, String> {
+    let raw = decode_header_path(required_header(headers, "x-path")?)?;
+    if raw.trim().is_empty() {
+        return Err("No file path given".to_string());
+    }
+    let path = PathBuf::from(&raw);
+    if !path.is_absolute() {
+        return Err("The export path must be absolute".to_string());
+    }
+    if bytes.is_empty() {
+        return Err("Nothing to write: the file is empty".to_string());
+    }
+    let parent = path.parent().ok_or_else(|| "The export path has no folder".to_string())?;
+    std::fs::create_dir_all(parent)
+        .map_err(|e| format!("Could not create {}: {e}", parent.display()))?;
+    write_atomic(&path, bytes)?;
+    conn.execute(
+        "UPDATE app_settings SET last_export_dir = ?1 WHERE id = 1",
+        params![parent.to_string_lossy()],
+    )
+    .map_err(|e| e.to_string())?;
+    Ok(raw)
+}
+
+pub fn get_last_export_dir_impl(conn: &Connection) -> Result<String, String> {
+    conn.query_row("SELECT last_export_dir FROM app_settings WHERE id = 1", [], |r| r.get(0))
+        .map_err(|e| e.to_string())
+}
+
+fn require_existing(path: &str) -> Result<PathBuf, String> {
+    if path.trim().is_empty() {
+        return Err("No file path given".to_string());
+    }
+    let path = PathBuf::from(path);
+    if !path.exists() {
+        return Err(format!("{} does not exist", path.display()));
+    }
+    Ok(path)
+}
+
+/// Last resort when the opener plugin cannot reach a file manager (a minimal Linux
+/// install has no D-Bus file-manager service or portal). Arguments are passed
+/// individually; nothing goes through a shell.
+fn reveal_fallback_command(path: &Path) -> Command {
+    #[cfg(target_os = "windows")]
+    {
+        let mut cmd = Command::new("explorer");
+        cmd.arg(format!("/select,{}", path.display()));
+        cmd
+    }
+    #[cfg(target_os = "macos")]
+    {
+        let mut cmd = Command::new("open");
+        cmd.arg("-R").arg(path);
+        cmd
+    }
+    #[cfg(not(any(target_os = "windows", target_os = "macos")))]
+    {
+        let folder = if path.is_dir() { path } else { path.parent().unwrap_or(path) };
+        let mut cmd = Command::new("xdg-open");
+        cmd.arg(folder);
+        cmd
+    }
+}
+
+fn open_fallback_command(path: &Path) -> Command {
+    #[cfg(target_os = "windows")]
+    let mut cmd = Command::new("explorer");
+    #[cfg(target_os = "macos")]
+    let mut cmd = Command::new("open");
+    #[cfg(not(any(target_os = "windows", target_os = "macos")))]
+    let mut cmd = Command::new("xdg-open");
+    cmd.arg(path);
+    cmd
+}
+
+fn spawn_detached(mut cmd: Command) -> Result<(), String> {
+    let mut child = cmd.spawn().map_err(|e| format!("Could not start the file manager: {e}"))?;
+    // Reap the child so it does not linger as a zombie; the result is irrelevant
+    // (explorer.exe, for one, exits non-zero even on success).
+    std::thread::spawn(move || {
+        let _ = child.wait();
+    });
+    Ok(())
+}
+
+#[tauri::command]
+pub async fn write_export_file(request: Request<'_>, state: State<'_, AppState>) -> Result<String, String> {
+    let bytes = raw_body(&request)?;
+    let headers = header_map(&request);
+    let conn = state.db.lock().map_err(|e| e.to_string())?;
+    write_export_file_impl(&conn, bytes, &headers)
+}
+
+#[tauri::command]
+pub fn get_last_export_dir(state: State<AppState>) -> Result<String, String> {
+    let conn = state.db.lock().map_err(|e| e.to_string())?;
+    get_last_export_dir_impl(&conn)
+}
+
+#[tauri::command]
+pub fn reveal_in_folder(app: tauri::AppHandle, path: String) -> Result<(), String> {
+    let path = require_existing(&path)?;
+    if app.opener().reveal_item_in_dir(&path).is_ok() {
+        return Ok(());
+    }
+    spawn_detached(reveal_fallback_command(&path))
+}
+
+#[tauri::command]
+pub fn open_file(app: tauri::AppHandle, path: String) -> Result<(), String> {
+    let path = require_existing(&path)?;
+    if app.opener().open_path(path.to_string_lossy(), None::<&str>).is_ok() {
+        return Ok(());
+    }
+    spawn_detached(open_fallback_command(&path))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::tempdir;
+
+    fn headers(path: &str) -> Headers {
+        Headers::from([("x-path".to_string(), path.to_string())])
+    }
+
+    fn encode(path: &Path) -> String {
+        percent_encoding::utf8_percent_encode(&path.to_string_lossy(), percent_encoding::NON_ALPHANUMERIC)
+            .to_string()
+    }
+
+    #[test]
+    fn writes_the_file_and_remembers_the_folder() {
+        let dir = tempdir().unwrap();
+        let conn = crate::db::open_in_memory().unwrap();
+        assert_eq!(get_last_export_dir_impl(&conn).unwrap(), "");
+
+        // Non-ASCII, spaces and a folder that does not exist yet.
+        let target = dir.path().join("New folder").join("\u{9ac}\u{9be}\u{982}\u{9b2}\u{9be} 1.pdf");
+        let written = write_export_file_impl(&conn, b"%PDF-1.7", &headers(&encode(&target))).unwrap();
+        assert_eq!(PathBuf::from(&written), target);
+        assert_eq!(std::fs::read(&target).unwrap(), b"%PDF-1.7");
+        assert_eq!(
+            get_last_export_dir_impl(&conn).unwrap(),
+            target.parent().unwrap().to_string_lossy()
+        );
+
+        // Overwrites in place.
+        write_export_file_impl(&conn, b"%PDF-2", &headers(&encode(&target))).unwrap();
+        assert_eq!(std::fs::read(&target).unwrap(), b"%PDF-2");
+    }
+
+    #[test]
+    fn rejects_empty_relative_and_missing_paths() {
+        let conn = crate::db::open_in_memory().unwrap();
+        for bad in ["", "   ", "out.pdf", "sub%2Fout.pdf", "..%2Fout.pdf"] {
+            assert!(write_export_file_impl(&conn, b"x", &headers(bad)).is_err(), "{bad}");
+        }
+        assert!(write_export_file_impl(&conn, b"x", &Headers::new()).is_err());
+        assert_eq!(get_last_export_dir_impl(&conn).unwrap(), "");
+    }
+
+    #[test]
+    fn rejects_an_empty_body_without_touching_the_folder_setting() {
+        let dir = tempdir().unwrap();
+        let conn = crate::db::open_in_memory().unwrap();
+        let target = dir.path().join("a.pdf");
+        assert!(write_export_file_impl(&conn, b"", &headers(&encode(&target))).is_err());
+        assert!(!target.exists());
+        assert_eq!(get_last_export_dir_impl(&conn).unwrap(), "");
+    }
+
+    #[test]
+    fn reveal_and_open_refuse_missing_paths() {
+        let dir = tempdir().unwrap();
+        assert!(require_existing("").is_err());
+        let missing = dir.path().join("nope.pdf");
+        assert!(require_existing(&missing.to_string_lossy()).unwrap_err().contains("does not exist"));
+        assert!(require_existing(&dir.path().to_string_lossy()).is_ok());
+    }
+
+    #[cfg(target_os = "linux")]
+    #[test]
+    fn linux_fallback_opens_the_parent_folder_with_separate_args() {
+        let dir = tempdir().unwrap();
+        let file = dir.path().join("a b; rm -rf.pdf");
+        std::fs::write(&file, b"x").unwrap();
+        let cmd = reveal_fallback_command(&file);
+        assert_eq!(cmd.get_program(), "xdg-open");
+        let args: Vec<_> = cmd.get_args().collect();
+        assert_eq!(args, [dir.path().as_os_str()]);
+        let open = open_fallback_command(&file);
+        assert_eq!(open.get_args().collect::<Vec<_>>(), [file.as_os_str()]);
+    }
+}
diff --git a/src-tauri/src/commands/invoice.rs b/src-tauri/src/commands/invoice.rs
index 7bfb3c2..7361c4a 100644
--- a/src-tauri/src/commands/invoice.rs
+++ b/src-tauri/src/commands/invoice.rs
@@ -17,7 +17,7 @@ const INVOICE_COLS: &str = "id, number, series_id, invoice_date, due_date, clien
     tax_type, tax_rate, cgst_amount, sgst_amount, igst_amount, total, amount_in_words,
     bank_account_id, bank_snapshot, signature_path, notes, status, created_at, updated_at,
     doc_type, reverse_charge, COALESCE(vendor_snapshot, ''), snapshot_origin, cancelled_at,
-    cancel_reason, archived_pdf_sha256, COALESCE(render_prefs, '')";
+    cancel_reason, archived_pdf_sha256, COALESCE(render_prefs, ''), archived_fingerprint, archived_at";
 
 fn map_invoice(row: &Row) -> rusqlite::Result<Invoice> {
     Ok(Invoice {
@@ -56,6 +56,8 @@ fn map_invoice(row: &Row) -> rusqlite::Result<Invoice> {
         cancel_reason: row.get(32)?,
         archived_pdf_sha256: row.get(33)?,
         render_prefs: row.get(34)?,
+        archived_fingerprint: row.get(35)?,
+        archived_at: row.get(36)?,
         items: Vec::new(),
     })
 }
diff --git a/src-tauri/src/commands/mod.rs b/src-tauri/src/commands/mod.rs
index ecd2d7c..e0316c5 100644
--- a/src-tauri/src/commands/mod.rs
+++ b/src-tauri/src/commands/mod.rs
@@ -1,5 +1,8 @@
+pub mod archive;
 pub mod assets;
 pub mod clients;
+pub mod files;
 pub mod invoice;
+pub mod raw;
 pub mod series;
 pub mod settings;
diff --git a/src-tauri/src/commands/raw.rs b/src-tauri/src/commands/raw.rs
new file mode 100644
index 0000000..d64d495
--- /dev/null
+++ b/src-tauri/src/commands/raw.rs
@@ -0,0 +1,92 @@
+//! Helpers for commands that take their payload as a raw IPC body (no base64).
+//!
+//! The webview sends `invoke(cmd, Uint8Array, { headers })`; Tauri hands the bytes over as
+//! `InvokeBody::Raw` and the headers as an `http::HeaderMap`. Header values must be visible
+//! ASCII (`HeaderValue::from_str` rejects anything else), so non-ASCII data such as file
+//! paths is percent-encoded by the caller.
+use percent_encoding::percent_decode_str;
+use std::collections::HashMap;
+use tauri::ipc::{InvokeBody, Request};
+
+/// Lower-cased header name to value; values that are not valid UTF-8 are dropped.
+pub type Headers = HashMap<String, String>;
+
+pub fn raw_body<'a>(request: &'a Request<'_>) -> Result<&'a [u8], String> {
+    match request.body() {
+        InvokeBody::Raw(bytes) => Ok(bytes),
+        InvokeBody::Json(_) => Err("Expected a raw binary request body".to_string()),
+    }
+}
+
+pub fn header_map(request: &Request<'_>) -> Headers {
+    request
+        .headers()
+        .iter()
+        .filter_map(|(name, value)| {
+            let value = value.to_str().ok()?;
+            Some((name.as_str().to_ascii_lowercase(), value.to_string()))
+        })
+        .collect()
+}
+
+pub fn required_header<'a>(headers: &'a Headers, name: &str) -> Result<&'a str, String> {
+    headers
+        .get(name)
+        .map(String::as_str)
+        .ok_or_else(|| format!("Missing {name} header"))
+}
+
+pub fn decode_header_path(value: &str) -> Result<String, String> {
+    percent_decode_str(value)
+        .decode_utf8()
+        .map(|s| s.into_owned())
+        .map_err(|_| "The path header is not valid UTF-8".to_string())
+}
+
+/// Write `bytes` to `path` via a sibling temp file and a rename, so a crash never leaves a
+/// half-written file under the final name.
+pub fn write_atomic(path: &std::path::Path, bytes: &[u8]) -> Result<(), String> {
+    use std::io::Write;
+    let mut tmp_name = path
+        .file_name()
+        .ok_or_else(|| "The path has no file name".to_string())?
+        .to_os_string();
+    tmp_name.push(".tmp");
+    let tmp = path.with_file_name(tmp_name);
+    let result = (|| {
+        let mut file = std::fs::File::create(&tmp)?;
+        file.write_all(bytes)?;
+        file.sync_all()?;
+        std::fs::rename(&tmp, path)
+    })();
+    if let Err(e) = result {
+        let _ = std::fs::remove_file(&tmp);
+        return Err(format!("Could not write {}: {e}", path.display()));
+    }
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::tempdir;
+
+    #[test]
+    fn decodes_percent_encoded_paths() {
+        assert_eq!(
+            decode_header_path("%2Ftmp%2Fa%20b%2F%E0%A6%AC.pdf").unwrap(),
+            "/tmp/a b/\u{9ac}.pdf"
+        );
+        assert!(decode_header_path("%FF").is_err());
+    }
+
+    #[test]
+    fn atomic_write_replaces_and_leaves_no_temp_file() {
+        let dir = tempdir().unwrap();
+        let target = dir.path().join("out.pdf");
+        write_atomic(&target, b"one").unwrap();
+        write_atomic(&target, b"two").unwrap();
+        assert_eq!(std::fs::read(&target).unwrap(), b"two");
+        assert_eq!(std::fs::read_dir(dir.path()).unwrap().count(), 1);
+    }
+}
diff --git a/src-tauri/src/commands/settings.rs b/src-tauri/src/commands/settings.rs
index bb8a006..10042a8 100644
--- a/src-tauri/src/commands/settings.rs
+++ b/src-tauri/src/commands/settings.rs
@@ -6,7 +6,7 @@ use tauri::State;
 pub(crate) const SETTINGS_COLS: &str = "vendor_name, vendor_address, vendor_email, vendor_phone, vendor_pan,
     vendor_gstin, vendor_state_code, logo_path, signature_path, default_bank_id, default_tax_rate,
     default_tax_type, payment_terms_days, currency, onboarded, theme, gst_registration, default_hsn_sac, signatory_name,
-    signatory_designation, render_prefs";
+    signatory_designation, render_prefs, last_export_dir";
 
 pub(crate) fn map_settings(row: &Row) -> rusqlite::Result<Settings> {
     Ok(Settings {
@@ -31,6 +31,7 @@ pub(crate) fn map_settings(row: &Row) -> rusqlite::Result<Settings> {
         signatory_name: row.get(18)?,
         signatory_designation: row.get(19)?,
         render_prefs: row.get(20)?,
+        last_export_dir: row.get(21)?,
     })
 }
 
diff --git a/src-tauri/src/db.rs b/src-tauri/src/db.rs
index 005ab49..38483bc 100644
--- a/src-tauri/src/db.rs
+++ b/src-tauri/src/db.rs
@@ -10,7 +10,7 @@ const MAX_BACKUPS: usize = 10;
 const BACKUP_PREFIX: &str = "voiced-pre-v";
 
 /// Highest schema version, i.e. the number of entries in `migrations()`.
-const LATEST_VERSION: i64 = 3;
+const LATEST_VERSION: i64 = 4;
 
 #[derive(Debug, thiserror::Error)]
 pub enum DbError {
@@ -174,8 +174,15 @@ const M3: &str = r#"
 ALTER TABLE app_settings ADD COLUMN render_prefs TEXT NOT NULL DEFAULT '';
 "#;
 
+/// Version 4: the archived PDF's layout fingerprint and time, and the last export folder.
+const M4: &str = r#"
+ALTER TABLE invoices ADD COLUMN archived_fingerprint TEXT;
+ALTER TABLE invoices ADD COLUMN archived_at TEXT;
+ALTER TABLE app_settings ADD COLUMN last_export_dir TEXT NOT NULL DEFAULT '';
+"#;
+
 fn migrations() -> Migrations<'static> {
-    Migrations::new(vec![M::up(SCHEMA), M::up(M2), M::up(M3)])
+    Migrations::new(vec![M::up(SCHEMA), M::up(M2), M::up(M3), M::up(M4)])
 }
 
 /// Open (creating if needed) the database at `path` and bring it to the latest schema.
@@ -541,6 +548,27 @@ CREATE INDEX IF NOT EXISTS idx_invoices_created ON invoices(created_at DESC);
         assert!(backups_in(&backups).is_empty());
     }
 
+    #[test]
+    fn m4_adds_archive_and_export_dir_columns() {
+        let conn = open_in_memory().unwrap();
+        let dir: String = conn
+            .query_row("SELECT last_export_dir FROM app_settings WHERE id = 1", [], |r| r.get(0))
+            .unwrap();
+        assert_eq!(dir, "");
+        // The columns exist and are nullable on invoices (no rows needed to prove it).
+        conn.prepare("SELECT archived_pdf_sha256, archived_fingerprint, archived_at FROM invoices")
+            .unwrap();
+        let notnull: i64 = conn
+            .query_row(
+                "SELECT SUM(\"notnull\") FROM pragma_table_info('invoices')
+                 WHERE name IN ('archived_fingerprint', 'archived_at')",
+                [],
+                |r| r.get(0),
+            )
+            .unwrap();
+        assert_eq!(notnull, 0);
+    }
+
     #[test]
     fn render_prefs_column_defaults_to_empty_and_round_trips() {
         let conn = open_in_memory().unwrap();
diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index ea171d4..97c200b 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -12,6 +12,9 @@ use tauri_plugin_dialog::{DialogExt, MessageDialogKind};
 pub struct AppState {
     pub db: Mutex<Connection>,
     pub data_dir: PathBuf,
+    /// Machine-local, non-roaming data (the PDF archive). On Windows this is
+    /// %LOCALAPPDATA%, unlike `data_dir`, which is the roaming location.
+    pub local_data_dir: PathBuf,
 }
 
 /// Show a native error dialog. Release builds have no console on Windows, so
@@ -40,6 +43,17 @@ fn init_state(app: &tauri::App) -> Result<AppState, Box<dyn std::error::Error>>
         show_startup_error(app, &format!("Could not create the application data directory: {e}"), Some(&data_dir));
         return Err(e.into());
     }
+    let local_data_dir = match app.path().app_local_data_dir() {
+        Ok(dir) => dir,
+        Err(e) => {
+            show_startup_error(app, &format!("Could not resolve the local data directory: {e}"), Some(&data_dir));
+            return Err(e.into());
+        }
+    };
+    if let Err(e) = std::fs::create_dir_all(&local_data_dir) {
+        show_startup_error(app, &format!("Could not create the local data directory: {e}"), Some(&local_data_dir));
+        return Err(e.into());
+    }
     let conn = match db::open(&data_dir.join("voiced.db"), &data_dir.join("backups")) {
         Ok(conn) => conn,
         Err(e) => {
@@ -54,6 +68,7 @@ fn init_state(app: &tauri::App) -> Result<AppState, Box<dyn std::error::Error>>
     Ok(AppState {
         db: Mutex::new(conn),
         data_dir,
+        local_data_dir,
     })
 }
 
@@ -113,7 +128,13 @@ pub fn run() {
             commands::assets::save_asset_bytes,
             commands::assets::read_asset_data_uri,
             commands::assets::remove_asset,
-            commands::assets::save_binary_file,
+            commands::archive::archive_pdf,
+            commands::archive::read_archive,
+            commands::archive::archive_status,
+            commands::files::write_export_file,
+            commands::files::get_last_export_dir,
+            commands::files::reveal_in_folder,
+            commands::files::open_file,
         ])
         .run(tauri::generate_context!());
 
diff --git a/src-tauri/src/models.rs b/src-tauri/src/models.rs
index eec9bc3..7ec9abe 100644
--- a/src-tauri/src/models.rs
+++ b/src-tauri/src/models.rs
@@ -26,6 +26,9 @@ pub struct Settings {
     /// The user's default page setup (RenderPrefsV1 JSON); empty means the built-in defaults.
     #[serde(default)]
     pub render_prefs: String,
+    /// Folder of the last export; owned by the backend, so saving settings never changes it.
+    #[serde(default)]
+    pub last_export_dir: String,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -199,6 +202,8 @@ pub struct Invoice {
     pub archived_pdf_sha256: Option<String>,
     /// RenderPrefsV1 JSON frozen at issue; empty when none was stored.
     pub render_prefs: String,
+    pub archived_fingerprint: Option<String>,
+    pub archived_at: Option<String>,
     pub items: Vec<InvoiceItem>,
 }
 
diff --git a/src/lib/api.ts b/src/lib/api.ts
index c9f4c0b..eec34fb 100644
--- a/src/lib/api.ts
+++ b/src/lib/api.ts
@@ -10,6 +10,13 @@ import type {
   Settings,
 } from "./types";
 
+export interface ArchiveStatus {
+  archived: boolean;
+  sha256?: string;
+  fingerprint?: string;
+  archivedAt?: string;
+}
+
 export const api = {
   getSettings: () => invoke<Settings>("get_settings"),
   saveSettings: (settings: Settings) => invoke<Settings>("save_settings", { settings }),
@@ -47,6 +54,19 @@ export const api = {
     invoke<string>("save_asset_bytes", { kind, fileName, dataBase64 }),
   readAssetDataUri: (path: string) => invoke<string>("read_asset_data_uri", { path }),
   removeAsset: (path: string) => invoke<void>("remove_asset", { path }),
-  saveBinaryFile: (path: string, dataBase64: string) =>
-    invoke<void>("save_binary_file", { path, dataBase64 }),
+
+  // Raw-body commands: the payload is the bytes themselves (no base64); metadata goes in headers.
+  // Header values must be visible ASCII, hence the encodeURIComponent on paths.
+  archivePdf: (invoiceId: number, bytes: Uint8Array, fingerprint: string) =>
+    invoke<string>("archive_pdf", bytes, {
+      headers: { "x-invoice-id": String(invoiceId), "x-fingerprint": fingerprint },
+    }),
+  readArchive: async (invoiceId: number): Promise<Uint8Array> =>
+    new Uint8Array(await invoke<ArrayBuffer>("read_archive", { invoiceId })),
+  archiveStatus: (invoiceId: number) => invoke<ArchiveStatus>("archive_status", { invoiceId }),
+  writeExportFile: (path: string, bytes: Uint8Array) =>
+    invoke<string>("write_export_file", bytes, { headers: { "x-path": encodeURIComponent(path) } }),
+  getLastExportDir: () => invoke<string>("get_last_export_dir"),
+  revealInFolder: (path: string) => invoke<void>("reveal_in_folder", { path }),
+  openFile: (path: string) => invoke<void>("open_file", { path }),
 };
diff --git a/src/lib/filename.test.ts b/src/lib/filename.test.ts
new file mode 100644
index 0000000..07180d1
--- /dev/null
+++ b/src/lib/filename.test.ts
@@ -0,0 +1,131 @@
+import { describe, expect, it } from "vitest";
+import { exportFileName, type ExportFileNameInput } from "./filename";
+
+const base: ExportFileNameInput = {
+  number: "AP-2026-001",
+  client: "Acme Ltd",
+  date: "2026-04-01",
+  mode: "searchable",
+};
+const name = (over: Partial<ExportFileNameInput> = {}) => exportFileName({ ...base, ...over });
+
+describe("exportFileName", () => {
+  it("uses number_client_date by default", () => {
+    expect(name()).toBe("AP-2026-001_Acme Ltd_2026-04-01.pdf");
+  });
+
+  it("turns a slash in the invoice number into a dash", () => {
+    expect(name({ number: "AP/2026-001" })).toBe("AP-2026-001_Acme Ltd_2026-04-01.pdf");
+  });
+
+  it("adds -flat for the flattened export", () => {
+    expect(name({ mode: "flattened" })).toBe("AP-2026-001_Acme Ltd_2026-04-01-flat.pdf");
+  });
+
+  it("honours a custom pattern", () => {
+    expect(name({ pattern: "{date} {client} {number}" })).toBe("2026-04-01 Acme Ltd AP-2026-001.pdf");
+    expect(name({ pattern: "{number}" })).toBe("AP-2026-001.pdf");
+  });
+
+  it("falls back to the default pattern for a blank pattern", () => {
+    expect(name({ pattern: "   " })).toBe(name());
+  });
+
+  it("replaces every Windows-forbidden character", () => {
+    expect(name({ client: 'A<B>C:D"E/F\\G|H?I*J' })).toBe("AP-2026-001_A-B-C-D-E-F-G-H-I-J_2026-04-01.pdf");
+  });
+
+  it("replaces control characters", () => {
+    expect(name({ client: "A\u0000B\tC\nD\u007fE" })).toBe("AP-2026-001_A-B-C-D-E_2026-04-01.pdf");
+  });
+
+  it("collapses runs of separators and spaces", () => {
+    expect(name({ client: "A///B   C___D" })).toBe("AP-2026-001_A-B C_D_2026-04-01.pdf");
+  });
+
+  it("trims dots and spaces from the ends", () => {
+    expect(name({ pattern: "  {client}. . " })).toBe("Acme Ltd.pdf");
+    expect(name({ pattern: "{client}", client: "Acme Ltd. " })).toBe("Acme Ltd.pdf");
+    expect(name({ pattern: "{client}", client: "...hidden" })).toBe("hidden.pdf");
+  });
+
+  it("drops the separators left behind by empty parts", () => {
+    expect(name({ client: "" })).toBe("AP-2026-001_2026-04-01.pdf");
+    expect(name({ client: "", date: "" })).toBe("AP-2026-001.pdf");
+  });
+
+  it("prefixes reserved device names", () => {
+    expect(name({ pattern: "{client}", client: "CON" })).toBe("_CON.pdf");
+    expect(name({ pattern: "{client}", client: "nul" })).toBe("_nul.pdf");
+    expect(name({ pattern: "{client}", client: "Aux" })).toBe("_Aux.pdf");
+    expect(name({ pattern: "{client}", client: "PRN" })).toBe("_PRN.pdf");
+  });
+
+  it("prefixes COM1-9 and LPT1-9 but not COM10 or lookalikes", () => {
+    expect(name({ pattern: "{client}", client: "COM1" })).toBe("_COM1.pdf");
+    expect(name({ pattern: "{client}", client: "com9" })).toBe("_com9.pdf");
+    expect(name({ pattern: "{client}", client: "LPT3" })).toBe("_LPT3.pdf");
+    expect(name({ pattern: "{client}", client: "COM10" })).toBe("COM10.pdf");
+    expect(name({ pattern: "{client}", client: "CONSOLE" })).toBe("CONSOLE.pdf");
+  });
+
+  it("catches a reserved name that has an extension-like tail", () => {
+    expect(name({ pattern: "{client}", client: "CON.txt" })).toBe("_CON.txt.pdf");
+  });
+
+  it("keeps Indic client names intact", () => {
+    expect(name({ client: "சென்னை ஸ்டூடியோ" })).toBe(
+      "AP-2026-001_சென்னை ஸ்டூடியோ_2026-04-01.pdf",
+    );
+    expect(name({ client: "ਭਾਰਤ/ਕੰਪਨੀ" })).toContain("ਭਾਰਤ-ਕੰਪਨੀ");
+  });
+
+  it("normalises Unicode to NFC", () => {
+    const decomposed = "Café";
+    expect(name({ pattern: "{client}", client: decomposed })).toBe("Café.pdf");
+  });
+
+  it("caps the stem at 120 characters and cuts the client first", () => {
+    const out = name({ client: "x".repeat(300) });
+    const stem = out.slice(0, -".pdf".length);
+    expect(stem.length).toBeLessThanOrEqual(120);
+    expect(out.startsWith("AP-2026-001_x")).toBe(true);
+    expect(out.endsWith("_2026-04-01.pdf")).toBe(true);
+  });
+
+  it("keeps the number whole even when it alone is long", () => {
+    const number = "N".repeat(110);
+    const out = name({ number, client: "y".repeat(200) });
+    expect(out.startsWith(number)).toBe(true);
+    expect(out.length).toBeLessThanOrEqual(120 + ".pdf".length);
+  });
+
+  it("hard-caps an absurdly long number", () => {
+    const out = name({ number: "9".repeat(500) });
+    expect(out.length).toBeLessThanOrEqual(120 + ".pdf".length);
+  });
+
+  it("does not split a surrogate pair when truncating", () => {
+    const out = name({ pattern: "{client}", client: "\u{1F600}".repeat(100) });
+    const stem = out.slice(0, -".pdf".length);
+    expect(stem.length).toBeLessThanOrEqual(120);
+    expect([...stem].every((ch) => ch === "\u{1F600}")).toBe(true);
+  });
+
+  it("adds -flat after truncation", () => {
+    const out = name({ client: "z".repeat(300), mode: "flattened" });
+    expect(out.endsWith("_2026-04-01-flat.pdf")).toBe(true);
+  });
+
+  it("uses a non-empty fallback", () => {
+    expect(name({ number: "", client: "", date: "" })).toBe("invoice.pdf");
+    expect(name({ pattern: "...", number: "x" })).toBe("invoice.pdf");
+    expect(name({ number: "///", client: "***", date: "|" })).toBe("invoice.pdf");
+    expect(name({ number: "", client: "", date: "", mode: "flattened" })).toBe("invoice-flat.pdf");
+  });
+
+  it("the result never ends in a dot or space", () => {
+    const out = name({ client: "Trailing dot.", date: "" });
+    expect(out).not.toMatch(/[. ]\.pdf$/);
+  });
+});
diff --git a/src/lib/filename.ts b/src/lib/filename.ts
new file mode 100644
index 0000000..e0173e2
--- /dev/null
+++ b/src/lib/filename.ts
@@ -0,0 +1,71 @@
+export type ExportMode = "searchable" | "flattened";
+
+export interface ExportFileNameInput {
+  /** Tokens: {number}, {client}, {date}. */
+  pattern?: string;
+  number: string;
+  client: string;
+  date: string;
+  mode: ExportMode;
+}
+
+const DEFAULT_PATTERN = "{number}_{client}_{date}";
+const MAX_STEM = 120;
+const FALLBACK = "invoice";
+
+// Characters Windows forbids in file names, plus control characters.
+// eslint-disable-next-line no-control-regex
+const FORBIDDEN = /[<>:"/\\|?*\u0000-\u001f\u007f]/g;
+// The device name matters even with an extension ("CON.txt" is still the console).
+const RESERVED = /^(con|prn|aux|nul|com[1-9¹²³]|lpt[1-9¹²³])$/i;
+const EDGE_JUNK = /^[.\s_-]+|[.\s_-]+$/g;
+
+function collapse(value: string): string {
+  return value
+    .replace(FORBIDDEN, "-")
+    .replace(/\s+/g, " ")
+    .replace(/-{2,}/g, "-")
+    .replace(/_{2,}/g, "_")
+    .replace(/ ?([-_]) ?/g, "$1");
+}
+
+function cleanPart(value: string): string {
+  return collapse(value.normalize("NFC")).replace(EDGE_JUNK, "");
+}
+
+/** Cut to at most `max` UTF-16 units without splitting a surrogate pair. */
+function truncate(value: string, max: number): string {
+  let out = "";
+  for (const ch of value) {
+    if (out.length + ch.length > max) break;
+    out += ch;
+  }
+  return out;
+}
+
+function fill(pattern: string, parts: { number: string; client: string; date: string }): string {
+  return pattern.replace(/\{(number|client|date)\}/g, (_, key: keyof typeof parts) => parts[key]);
+}
+
+/** A file name that is valid on Windows, macOS and Linux for an exported invoice PDF. */
+export function exportFileName(input: ExportFileNameInput): string {
+  const pattern = input.pattern?.trim() ? input.pattern : DEFAULT_PATTERN;
+  const parts = {
+    number: cleanPart(input.number),
+    client: cleanPart(input.client),
+    date: cleanPart(input.date),
+  };
+
+  let stem = fill(pattern, parts);
+  if (stem.length > MAX_STEM) {
+    // The invoice number is what identifies the file, so the client name gives way first.
+    const overflow = stem.length - MAX_STEM;
+    const client = truncate(parts.client, Math.max(0, parts.client.length - overflow));
+    stem = fill(pattern, { ...parts, client });
+  }
+  stem = cleanPart(truncate(cleanPart(stem), MAX_STEM));
+  if (!stem) stem = FALLBACK;
+  if (RESERVED.test(stem.split(".")[0])) stem = `_${stem}`;
+
+  return `${stem}${input.mode === "flattened" ? "-flat" : ""}.pdf`;
+}
diff --git a/src/lib/pdf.tsx b/src/lib/pdf.tsx
index ee76b95..9dfba74 100644
--- a/src/lib/pdf.tsx
+++ b/src/lib/pdf.tsx
@@ -10,13 +10,6 @@ import { imageSizeFromDataUri } from "./imageSize";
 import { getRenderClient, nextRenderJobId } from "./renderClient";
 import type { BankAccount, Invoice, Settings } from "./types";
 
-function bytesToBase64(bytes: Uint8Array): string {
-  let bin = "";
-  const step = 0x8000;
-  for (let i = 0; i < bytes.length; i += step) bin += String.fromCharCode(...bytes.subarray(i, i + step));
-  return btoa(bin);
-}
-
 /** A logo with no readable size is fitted as if it filled Classic's 170 x 54 box. */
 const UNKNOWN_LOGO_SIZE = { width: 170, height: 54 };
 
@@ -82,7 +75,7 @@ export async function savePdfBytes(bytes: Uint8Array, fileName: string): Promise
     filters: [{ name: "PDF document", extensions: ["pdf"] }],
   });
   if (!path) return null;
-  await api.saveBinaryFile(path, bytesToBase64(bytes));
+  await api.writeExportFile(path, bytes);
   return path;
 }
 
diff --git a/src/lib/types.ts b/src/lib/types.ts
index cc01864..fd4eb8e 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -25,6 +25,8 @@ export interface Settings {
   signatoryDesignation: string;
   /** The user's default page setup (RenderPrefsV1 JSON); empty means the built-in defaults. */
   renderPrefs: string;
+  /** Folder of the last export; kept by the backend (saving settings does not change it). */
+  lastExportDir?: string;
 }
 
 export interface BankAccount {
@@ -136,6 +138,9 @@ export interface Invoice {
   archivedPdfSha256: string | null;
   /** RenderPrefsV1 JSON frozen at issue; empty when none was stored. */
   renderPrefs: string;
+  /** Layout fingerprint of the archived PDF; null when nothing is archived. */
+  archivedFingerprint?: string | null;
+  archivedAt?: string | null;
   items: InvoiceItem[];
 }