How to password-protect a PDF

Password protection stops the wrong people from opening — or changing — your PDF. There are actually two different passwords in the PDF spec, and knowing the difference matters.

Open password vs permissions password

• Open (user) password — required to view the document at all. Without it, the content is encrypted and unreadable.
• Permissions (owner) password — the file opens freely, but printing, copying, or editing are restricted unless you supply it.

The open password is the strong one, because it's tied to real encryption. Permissions restrictions are more of a polite request that well-behaved readers honour but determined tools can bypass.

Choosing a good password

• Long beats complex — a passphrase of several words is strong and memorable.
• Don't reuse a password you use elsewhere.
• Share the password over a different channel than the file itself (e.g. file by email, password by text).

Where it happens matters

Encrypting a sensitive file on someone else's server is a contradiction. Prefer a tool that encrypts locally. FreshPDF derives a key from your password and encrypts the file with AES-256 right in your browser, so the plaintext never leaves your device.