Security and privacy

How to Password Protect a PDF With AES-256

Updated 2026-09-17 · 2 min read

PDF security has two separate parts that get confused constantly: the password required to open the file, and the permissions controlling what someone can do once it is open.

Here is what each one protects against, and how to set both.

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Open passwords

An open password encrypts the file contents with AES-256. Without the password the file is unreadable — this is real cryptography, not a flag. Choose a long passphrase and send it through a different channel from the document itself.

Permissions

Permissions can disallow printing, copying text or further editing. Well-behaved PDF readers respect them; determined users with the right software can bypass them. Treat permissions as a clear instruction, not a lock.

Practical advice

For genuinely sensitive documents — payslips, medical letters, contracts — use an open password. For internal drafts, restricting editing is usually enough. Never rely on permissions alone for confidential data.

Frequently asked

Can I remove a password?

Yes, if you can already open the file with the correct password.

Is AES-256 strong enough?

Yes. The weak link is always the passphrase, not the algorithm.

Will encrypted PDFs open on a phone?

Yes, the reader prompts for the password.

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