Password protecting a PDF: what it actually stops

PDF protection comes in two flavours, and they offer very different levels of security.

Open password

The file is encrypted. Without the password, the content is unreadable, even to software that ignores rules. This is real protection. Protect PDF with Password uses AES with a 128 bit key, which every mainstream reader supports.

Its strength depends entirely on your password. A short dictionary word can be brute forced offline. A passphrase of four unrelated words cannot, in any practical sense.

Permissions password

The file opens for anyone, but flags tell readers to block printing, copying or editing. Adobe Reader and other well behaved software honour those flags. Plenty of other software ignores them, and anyone can photograph the screen. Restrict PDF Printing and Copying is a polite request, not a lock.

Use it to stop casual reuse of a price list. Do not use it for anything confidential.

Sending the password

Emailing a locked file and its password in the same thread defeats the purpose. Send the file by email and the password by another route, such as a phone call or a message. If the recipient loses it, no one can recover the file, including us.

When a PDF password is the wrong tool

If you are protecting a whole set of files, encrypting each one is tedious. Password Protected ZIP wraps many files in one AES-256 archive. For a single file of any type, Encrypt File with Password uses AES-256-GCM with a slow key derivation step that makes guessing far more expensive.

Removing a password

Remove PDF Password works when you know the password. It decrypts the file so other tools can read it. We do not provide any way to open a file whose password you do not have, and be wary of sites that claim to.

One practical note: encrypt last. Compression, merging and page numbering all need to read the file, so lock it once the document is final.