Add a password to a PDF with 256-bit AES encryption, entirely in your browser. Set the
password, download the protected file, and share it knowing the contents can’t be opened
without it — and knowing your document was never uploaded to do it.
How to password-protect a PDF
- Drop or choose the PDF you want to protect.
- Enter the password that will be required to open it.
- Click Protect PDF and download the encrypted copy.
The first run loads the PDF engine (about 1 MB); after that it’s instant.
Why doing this in the browser matters
Encrypting a PDF on someone else’s server means handing them the very document you’re trying to
keep private — before it’s protected. This tool avoids that entirely: it runs qpdf
(a mature, open-source PDF engine) compiled to WebAssembly, so the encryption happens on your
own device and neither the file nor the password is transmitted. For a security tool, that’s
not a nice-to-have — it’s the whole point.
Choose the password carefully
AES-256 is effectively unbreakable by brute force — but only as strong as the password in front
of it. A dictionary word or a short PIN can be guessed no matter how good the encryption is. Use
a long, unique password (a password manager makes this painless), and store it somewhere safe:
there is no recovery if you forget it. To take a password back off a PDF you can already
open, use the unlock PDF tool.
Private by design
The encryption runs on your device via WebAssembly. Your PDF and password never leave the
browser, and nothing is stored.
Frequently asked questions
- How strong is the encryption?
- This tool applies 256-bit AES encryption — the modern standard used by PDF software and considered secure when paired with a strong password. The weak link is never the algorithm; it's the password. A short or guessable one undermines even the strongest encryption, so choose a long, unique password.
- Is my PDF uploaded to a server?
- No. The PDF is encrypted entirely in your browser using qpdf compiled to WebAssembly — your file and your password never leave your device. That's essential for a security tool: a "protect PDF" service that uploads your document to encrypt it has already seen the contents you're trying to protect.
- What's the difference between an open password and permissions?
- An open (user) password is required to view the document at all — that's what this tool sets. Some PDFs also use an owner password to restrict printing or copying while still opening freely; those restrictions are advisory and widely ignored by viewers. An open password is the one that actually keeps people out.
- What if I forget the password?
- There is no recovery — that's the point of real encryption. If you lose the password, the PDF is unrecoverable by you or anyone else. Store it in a password manager. To remove a password you still know, use the unlock tool.
- Will the protected PDF open everywhere?
- Yes — AES-256 encrypted PDFs open in every modern PDF reader (Acrobat, Preview, browsers, phones); the reader simply prompts for the password. Very old readers may not support AES-256, but that's rare today.