How secure is PDF password protection?

With AES-256 and a strong password it's very secure. Weak passwords are the real risk, because they can be guessed.

Can I password protect a PDF on my phone?

Yes. Open the tool in your phone's browser, pick the PDF from your files and download the protected copy.

How do I remove the password later?

Use Unlock PDF with the password to save an unprotected copy.

How to password protect a PDF

A password-protected PDF can't be opened without the password, even if the file is forwarded or leaked. Here's how to add one in a minute without paying for Acrobat.

Open Protect PDF

Steps

Open Protect PDF and drop your file.
Enter a strong password and confirm it.
Choose whether the PDF can be printed, copied or edited once opened.
Click Protect & download — the new copy asks for the password.

Open password vs permissions password

The open (user) password encrypts the file, so nobody can read it without that password. The permissions (owner) password only controls what people can do after opening it, such as printing or copying. Mainstream PDF apps respect permissions, but some software ignores them — rely on the open password for real protection.

Share the password safely

Send the password separately from the file — for example by text message if you emailed the PDF.
Use a long, unique password rather than a date of birth for anything sensitive.
Keep an unprotected original: a forgotten password can't be recovered.

Tools used in this guide

Protect PDFAdd a password to a PDF with AES-256 Unlock PDFRemove a PDF password you know Compress PDFReduce PDF file size