Password protect your PDF
Add a password to a PDF — right in your browser.
AES-256 encryption, granular permissions, no upload.
Click below to set a password and configure permissions.
Set the PDF password
Your password stays in your browser. We never see it.
Protect multiple PDFs at once with Pro
Free tier protects one file at a time. Upgrade to batch-protect dozens of files in one go — same key unlocks every Pro tool.
Get ProAlready have a Pro key? Paste it here
Protect multiple PDFs at once with Pro
Free tier protects one file at a time. Upgrade to batch-protect dozens of files in one go — same key unlocks every Pro tool.
Get ProAlready have a Pro key? Paste it here
About PDF protection
PDF password protection is the standard way to keep a document private. The PDF specification supports two passwords (a user password to open the file, and an owner password to change permissions or remove the protection) plus six permission flags (print, modify, extract text, annotate, fill forms, assemble pages). pdfmundo's Protect PDF tool sets these in your browser via qpdf compiled to WebAssembly. Your file and your password never travel to a server. We can't see either, and we can't recover the password if you forget it — that's a property of AES encryption, not a policy choice. Save the password somewhere safe before sharing the protected file.
Frequently asked questions
- Is my password safe?
- Yes. Your password is processed entirely in your browser. It's never uploaded, never stored, and never leaves your device. We can't see it.
- What if I forget the password?
- Then nobody can open the PDF — not us, not Adobe, not anyone. AES encryption is one-way without the key. Save your password somewhere safe before sharing the encrypted file.
- What's the difference between user and owner passwords?
- The user password is required to open the PDF. The owner password is required to change permissions or remove the protection. By default we set both to the same value; toggle 'Set a different owner password' if you want them separate.
- Will the protected PDF lose quality?
- No. Encryption is lossless. Pages, fonts, images, signatures, and embedded data are preserved exactly. Only access is restricted.
- What's the maximum file size?
- 25 MB on the free plan, 100 MB on Pro. The actual limit is your device's memory — older mobile devices may struggle on very large files.
- Does this work for all PDFs?
- Yes for any standard PDF. If your input PDF is already password-protected, you'll need to remove the password in your PDF software first — then come back to set a new password.
- Which encryption algorithm does this use?
- AES-256 by default (modern PDF 2.0 standard). AES-128 is available under 'Advanced settings' for compatibility with viewers older than Adobe Reader 9 (released 2008).
- Do I need an account?
- No. The tool is completely free to use without signing up.