Protect PDF with Password
Add password protection to your PDF files. For locked PDFs, unlock them first and optionally re-protect. Free, instant, and browser-based. No server uploads. Your documents stay private.
Drop files here or browse
Supports PDF - up to 50 MB
How PDF password protection actually works here
Adding a password runs RC4 128-bit encryption over the PDF's internal structure, using a lightweight in-browser library rather than a server round-trip. Encrypting sets the same password as both the "user" password (needed to open the file at all) and the "owner" password some PDF readers use to gate permissions like printing or copying — this tool doesn't currently offer a separate, weaker permissions-only password.
Unlocking works differently from encrypting: instead of just stripping an encryption flag, the tool loads the document with your password via PDF.js, then reassembles the pages into a fresh, genuinely unencrypted PDF using pdf-lib. That two-step approach — read with one library, rebuild with another — is why unlocking can also be the first step before re-protecting a PDF with a new password, or before running it through the compressor, which can't process an encrypted file directly.
Which situation, which approach
| Situation | Approach | Why |
|---|---|---|
| A PDF with sensitive info going over email | Add a password here before sending | Email itself is not encrypted end-to-end, so a password on the file is an extra layer if the message is forwarded or lands in the wrong inbox. |
| You received a locked PDF and forgot the password | This tool can’t help — only re-derive it if you know a candidate | RC4 protection is not reversible without the password; there is no recovery or brute-force feature here, by design. |
| A locked PDF you have the password for, that you want to share unprotected | Unlock with the password, then download or re-protect with a new one | Unlocking rebuilds the document via pdf-lib rather than just stripping a flag, so the output is a genuinely unencrypted file. |
| You need enterprise-grade AES-256, not RC4 | Use desktop Acrobat or a tool that specifically offers AES | This tool only implements RC4 128-bit — accurate and functional, but not the strongest standard available if your policy requires AES. |
Known limits
RC4 128-bit is an older encryption standard than the AES-256 that current desktop Acrobat defaults to. It's functional and widely compatible, but if your organization's policy specifically requires AES, use a tool that offers it instead.
There is no password recovery here, intentionally — if you forget the password on a PDF you protected, or receive a locked PDF without its password, this tool cannot open it. That is a property of encryption working correctly, not a missing feature.
Frequently asked questions
Is my PDF uploaded to a server?
No — and that matters more here than on most tools, since the file involved is one you specifically decided needs protecting. Encryption runs via an in-browser library, unlocking via PDF.js and pdf-lib, both entirely client-side. You can confirm this in your browser’s Network tab: no request carrying your file or your password fires at any point.
What type of encryption is used?
We use RC4 128-bit encryption, which is compatible with all major PDF readers including Adobe Acrobat, Preview, and browser-based viewers.
Can I remove the password later?
Once a PDF is password-protected, you will need the password to open it. There is no way to remove the password without the correct password.
Can I also unlock password-protected PDFs here?
Yes. If you upload a password-protected PDF, you will be prompted to enter the password. After unlocking, you can add a new password or download it unprotected.
Is there a minimum password length?
Yes — 6 characters minimum, checked before encryption runs. Longer, less guessable passwords are still worth using: RC4 128-bit protects against casual access, not a determined attacker with password-cracking tools, since the algorithm itself (unlike AES-256) is decades old.
Does this set an owner password and a user password separately?
No. This tool applies the same password as both the user password (required to open the file) and the owner password (which controls permissions like printing or copying in PDFs that support that distinction). There is no separate "view but don’t edit" mode.