How to password protect a PDF (and which password you need)

Most people who protect a PDF set the wrong password, then wonder why the recipient could print it anyway. The format supports two, and only one of them actually locks anything.

The confusion is baked into the format. A PDF can carry an open password, a permissions password, or both, and software tends to present them as two checkboxes with no explanation of the gulf between them.

The open password encrypts the file

An open password — sometimes called a user password — encrypts the document's contents. Without it there is nothing to read: not the text, not the images, not the page count. Every reader on every platform will refuse, because there is genuinely nothing there until the password decrypts it.

This is real protection, and it is what you want any time the file leaves your hands. A payslip going to a mortgage broker, a contract going by email, an ID scan going to a letting agent — if the message reaches the wrong inbox, an open password means the attachment is useless to whoever opens it.

The permissions password only asks

A permissions password — an owner password — leaves the document fully readable and sets flags requesting that readers disallow printing, copying or editing. Nothing is encrypted. The flags are a note to the software, and software is free to ignore the note.

Well-behaved readers honour it. Plenty of others do not, and stripping the flags takes seconds. Treat a permissions password as a clear statement of intent — useful for signalling that a document is not to be altered — and never as a guarantee.

If you only remember one thing: a permissions password does not stop anybody who does not want to be stopped. An open password stops everybody, including you.

Choosing a password that is worth setting

• Length beats complexity. Four unrelated words are stronger than eight scrambled characters, and far easier to read out over the phone.
• Never send the password in the same email as the file. Splitting them across two channels is the entire point of the exercise.
• Do not derive it from the document. A statement protected with the recipient's date of birth is protected with something printed inside it.
• Write it down somewhere before you send anything. There is no reset.

How to do it

1. 1Open Protect PDF and add the document.
2. 2Set an open password if the file must be unreadable without it. Add a permissions password only if you also want to signal that it should not be edited.
3. 3Save the protected copy, and keep your unprotected original.
4. 4Send the password separately — a different channel, ideally a different day.

The work happens in your browser, so the document and the password never leave your device. That matters more here than almost anywhere: uploading a file to a website in order to protect it means handing the unprotected version to a stranger first. If you want to see what other sites do with your uploads, we went through that in detail.

There is no recovery, and that is the point

Nobody can open an encrypted PDF without its password — not the site that made it, not Adobe, not a support desk. Encryption with a back door is not encryption. Keep the original unprotected file somewhere safe and treat the protected one as the copy you send.

Already have a locked file you can open and want rid of the prompt? That is the opposite job — Unlock PDF writes an unprotected copy of a document you can already read.

Common questions

Which password should I use for an email attachment?

The open password. It encrypts the file, so a message delivered to the wrong address is unreadable. A permissions password would leave the attachment open to anyone who received it.

Can the person I send it to remove the password?

Yes, once they can open it — and that is normal. Protection covers the file in transit; it was never a way to control what the recipient does afterwards.

What encryption does a PDF actually use?

Modern PDFs use AES, normally with a 256-bit key. The weak point is essentially never the algorithm — it is a short or guessable password.