Protect PDF — Add a Password, 256-bit AES
Encrypt a PDF with 256-bit AES right in your browser — user and owner passwords, printing and copying restrictions, zero upload.
Protect PDF
Add a password — 256-bit AES, in your browser
Encryption is 256-bit AES (PDF 2.0). Uncheck a box to restrict that action for people who only have the open password. Keep your password somewhere safe — there is no recovery, by design.
How to password-protect a PDF in your browser
- Choose the PDF you want to protect.
- Set the password — this is the one anyone needs to open the file. Optionally set a different owner password, which controls the document's permissions.
- Decide what readers may do: printing and text copying are allowed by default; uncheck either to lock it down.
- Hit Encrypt & Download. The new, encrypted file is built in your tab and saved by you — the unprotected original stays on your device, as it always was.
What does 256-bit AES actually mean?
It is the strongest encryption class the PDF format defines (PDF 2.0 / R6), the same algorithm class that banks and governments use for data at rest. Cracking it by force is not a realistic threat; the realistic threat is a guessed or shared password — which is why the tool pushes you toward a real one rather than "123456".
What's the difference between the two passwords?
The user password opens the document. The owner password controls the permission set (print, copy, …) and lets the document be re-opened with full rights. If you leave the owner password empty, it defaults to the user password. Many everyday uses only need the first one.
Why encrypt in the browser instead of uploading to a site?
Because a password-protecting service that takes your file by upload must trust that service with both the document and, in some designs, the password. Here the encryption is computed by a local WASM build of qpdf on your machine: the bytes of your document and your password never cross the network at any point. Open the network panel while you encrypt — nothing leaves.
Will the protected PDF open everywhere?
Yes. AES-256 PDFs open in every current reader — Adobe, Preview, Chrome, Edge, mobile PDF apps. Very old readers (pre-2006 era) cannot open them, which is an acceptable cost for the strongest protection the format offers.
Is there a "forgot password"?
No, and that is the point: with AES-256 the only honest answer is that the key is the password. The tool warns you about this at the moment it matters. If you lose the password, re-protect the original file (which you still have) with a new one.
FAQ
- Is my file uploaded to a server? No. The tool runs entirely in your browser — your file never leaves your device. You can verify it yourself: open the network panel and there is no upload request while you work.
- Do I need an account, and is it free? No account and no cost. It is free to use — no signup, no paywall, no daily limit.
- Which browsers does it work in? Any modern browser — Chrome, Edge, Firefox and Safari — on desktop or mobile.
- Is there a size limit? There is no server-side limit because nothing is uploaded. Practical limits come from your device's memory, which comfortably covers normal documents and photos.
- Does it work with encrypted PDFs? Standard PDFs work in every tool. If a file is password-protected, Unlock PDF opens it for you when you have the password, and Protect PDF applies a new 256-bit AES password. No tool bypasses encryption without the key.
Last updated: November 02, 2026 · By Saad, Founder of ToolWow