About Protect PDF
Protect PDF adds an open password using AES-256 encryption, the strongest standard PDF encryption. Anyone who opens the file in Adobe Reader, a browser or Preview will be asked for the password.
How to use Protect PDF
- Add the PDF you want to protect.
- Enter a password of at least 4 characters — longer is much safer.
- Press Protect PDF.
- Download the protected file and test that it asks for the password.
Tips for better results
- Send the password by a different route from the file — for example the PDF by email and the password by text message.
- Use a long passphrase of three or four random words rather than a short password.
- Keep an unprotected copy somewhere safe; a forgotten password can't be recovered.
Limitations
Files that already have a password must be unlocked first. The protected file also blocks editing and copying in viewers that respect PDF permissions.
Frequently asked questions
How secure is it?
It uses AES-256 encryption. The real-world protection mostly depends on choosing a long, unguessable password.
Can you recover my password if I forget it?
No. We never see your password or file.
Is my password or file uploaded?
Your file is processed by your own browser. It is not uploaded to our servers, and closing the tab clears it from memory.
Guide last reviewed 28 October 2026 by the ModernExpert.AI team.