Password protect PDF
AES-256 encryption that runs entirely in your browser. Set a password, restrict what readers can do, download — without uploading anything.
Password protect PDF encrypts your PDF with AES-256 (the same algorithm the NSA approved for TOP SECRET data) entirely in your browser, with qpdf compiled to WebAssembly — no upload, no daily limit. Set an open password, choose what readers can print, copy, edit, or fill in (4 toggles map to PDF spec permission flags), optionally set a separate owner password for fine-grained control. Output works in Acrobat, Preview, browser PDF viewers — anywhere the PDF spec is supported.
What is Password Protect PDF?
Password protect PDF encrypts the contents of a PDF using AES-256, the same standard published in NIST FIPS 197 and used by U.S. federal agencies for classified information up to TOP SECRET. Without the password, the file is unreadable — pages are stored as encrypted byte streams that no PDF reader can render. With the password, it's a normal PDF: opens in Adobe Acrobat, Preview, browser PDF viewers, anywhere.
Beyond the open password, you can pin down what readers are allowed to do once the file is open. Block printing, block text and image extraction, prevent edits, or restrict everything except form filling. These restrictions are enforced by every spec-compliant reader; the four toggles map directly to the permission flags written into the PDF's encryption dictionary. Pikowl runs the entire encryption locally using qpdf compiled to WebAssembly — your file never touches a server.
How does the encryption work?
We use qpdf — the standard open-source command-line PDF library — compiled to WebAssembly. When you click Encrypt, the file is loaded into a virtual filesystem inside a Web Worker, qpdf encrypts it with AES-256 using your password, and the result is written back as a Blob you download. The wasm binary is ~1.5 MB and only loads on first use, so the page itself stays small.
How strong is AES-256?
AES-256 (Advanced Encryption Standard, 256-bit key) is the same algorithm specified in NIST FIPS 197 and approved by the U.S. National Security Agency for protecting TOP SECRET data. PDF 2.0 (ISO 32000-2) uses AES-256 with a key derived from your password through a stretching function (PBKDF2-style), making brute-force attacks computationally expensive. A 12-character password with mixed case, digits, and symbols would take longer than the age of the universe to crack with current hardware.
How the four permission toggles map to the PDF spec
Each permission maps to a flag in the PDF encryption dictionary, defined by ISO 32000-2 §7.6.4. Allow printing sets the print flag. Allow copying sets the content-extraction flag. Allow editing sets the modify-content flag. Allow form filling sets the fill-forms flag (which is automatically granted when editing is allowed). Spec-compliant readers — Acrobat, Preview, browser PDF viewers — all honour these flags. The open password is the cryptographic protection; the permission flags are the policy layer on top.
Is it safe?
The PDF and your password never leave your browser. The qpdf wasm runtime executes inside a Web Worker; the file lives only as a Uint8Array in memory; encryption happens via standard PDF byte-stream rewriting; the result is handed back as a downloadable Blob. Open your browser's Network tab while encrypting — you'll see zero requests to our servers. The only network call is the one-time fetch of the wasm binary itself, which then caches.
Limits and behaviour
Maximum file size: 100 MB. Maximum password length: 127 characters (PDF spec hard cap). Encryption uses AES-256 (PDF 2.0 / ISO 32000-2). Permission flags follow the standard 4-bit model. Output is a single PDF; metadata is preserved; pages, layout, and content remain identical to the input.
Common Uses
- Sharing financial statements: Send tax returns, payroll summaries, or invoices over email with an open password — the recipient can read but not modify.
- Confidential contracts and NDAs: Add a password before forwarding a signed agreement, even between trusted parties, to prevent accidental forwarding to wider audiences.
- Client deliverables: Lock printing and editing on draft work-products to prevent unauthorised redistribution while you're still iterating.
- Patient records and medical reports: HIPAA-aligned protection for documents emailed between providers — encryption stays with the file even after it leaves your network.
- Educational materials: Distribute exam papers, lecture slides, or teacher resource packs with copy-protection enabled to deter sharing on assignment-help sites.
- Press kits and embargoed content: Lock previews, screenshots, and press releases with a password until the embargo lifts; share the password at the agreed time.
FAQ
Is AES-256 actually secure?
Yes. We use AES-256 — the same standard the U.S. government uses for TOP SECRET data. The key is derived from your password using a slow stretching function, making brute-force attacks computationally infeasible against any password longer than 8–10 mixed characters.
Is my PDF uploaded anywhere?
No. The encryption runs entirely in your browser via qpdf compiled to WebAssembly. Your file is never sent to our servers — there's nothing to upload, leak, or breach. You can verify this in your browser's Network tab.
What happens if I lose the password?
If you forget the open password, the file is unrecoverable — that's the whole point of strong encryption. There's no backdoor, no "forgot password" link. Save it in a password manager before encrypting.
What's the difference between user and owner passwords?
The owner password lets you change permissions or remove encryption later without knowing the open password. Most users only need one password — leave the owner field blank and we'll use the same password for both.
Will my encrypted PDF open in old PDF readers?
PDF 2.0 readers (Adobe Acrobat 9+, modern Preview, modern browser viewers) all support AES-256. Older readers (pre-2008) may need AES-128 — let us know via feedback if you need a legacy mode.
How well are the permission flags enforced?
The permission flags (print, copy, edit, fill forms) are enforced by spec-compliant PDF readers. They're a strong deterrent — Acrobat, Preview, browsers all honour them — but determined users with a custom PDF parser can bypass them. The open password is the cryptographically strong layer.
Is there a file size limit?
Pikowl handles up to 100 MB per file. The encryption itself is fast — a 50 MB PDF typically encrypts in under 5 seconds. The wasm runtime adds ~1.5 MB on first use, then caches.