What this tool does
Protect PDF encrypts your PDF with a password using the same standard security handler built into the PDF format itself (AES-256 or legacy RC4), so any PDF reader that respects PDF encryption will ask for the password before opening it. Everything runs locally in your browser tab — there's no upload and no server.
How to use it
- Drop a PDF onto the box above.
- Set a password, and optionally a separate owner password.
- Choose AES-256 (recommended) or RC4, then click Protect PDF.
Limitations
This tool refuses a PDF that's already password-protected — unlock it first with Unlock PDF, then re-protect it if needed. There is no password recovery: this tool doesn't store your password anywhere, so losing it means losing access permanently.
Frequently asked questions
Which algorithm should I choose?
AES-256 is the modern, strong default and works in any current PDF reader. RC4 is a weaker, legacy option kept only for opening in very old software that doesn't support AES-256 — use it only if you know you need it.
What happens if I forget the password?
The password is never sent anywhere and isn't stored by this tool — there is no recovery. Losing it means losing access to the protected file, so keep a copy of the original and the password somewhere safe.
What's the difference between the user and owner password?
The user password is required to open and read the file. The owner password (if you set a different one) controls permissions like printing or editing in readers that enforce them — most people can leave it blank to use the same password for both.