How to password-protect a PDF for free (Mac, Windows, phone)

Adobe would like this to require a subscription. It doesn't. Every mainstream operating system can already encrypt a PDF with software you have, and one free desktop app does it with stronger encryption than Acrobat's default. Here are the four routes, what encryption each actually gives you, and — more usefully — the two ways a PDF password quietly fails to protect anything.

Which method, in one table

Method 1: macOS Preview

The fastest route if you have a Mac, with nothing to install. The one thing people miss is that this lives under Export, not Save — the Save dialog has no encryption option at all, which is why so many people conclude Preview can't do it.

1. Open the PDF in Preview. Double-click the file on any Mac — Preview is the default PDF app and needs nothing installed.
2. Choose File → Export as PDF. Use Export, not Save. The Save dialog has no encryption option; Export is where the permissions live.
3. Click Permissions and set a password. Tick “Require password to open document” and type your password twice. You can also separately restrict printing and copying.
4. Save as a new file, then verify. Keep the unlocked original under a different name. Close the new file, reopen it, and confirm it actually asks for the password before you send it anywhere.

Method 2: Microsoft Word

Works when you still have the source document rather than only a PDF. Go to File → Save As, pick PDF as the format, then click Options and tick Encrypt the document with a password. You get AES-128.

The limitation is real: Word can only do this while producing a PDF. If someone sent you a finished PDF, Word can't encrypt it without converting it first, which will rearrange your layout. Use Preview or LibreOffice for those.

Method 3: LibreOffice (the strongest free option)

Free, open source, runs on everything, and recent versions do AES-256 — stronger than what Preview or Word produce. Open the PDF, choose File → Export as PDF, open the Security tab, click Set Passwords, and set an open password.

Worth the download if you do this regularly, or if a client has specified 256-bit encryption. For a one-off on a Mac, Preview is quicker and AES-128 is not a weak link.

Method 4: Online tools — read this first

They work, and they're convenient. But look at what the transaction involves: you upload an unencrypted confidential document to someone else's server so that it can be encrypted there, and you hand that server your password as well. Reputable services delete files after an hour and say so. You are still trusting a third party with exactly the document you decided was too sensitive to send in the clear.

The two ways a PDF password fails you

1. You set the wrong kind of password

PDFs support two passwords and they are not remotely equivalent:

• Open password (user password) — the file is genuinely encrypted. Without the password there is nothing readable on disk. This is the one you want.
• Permissions password (owner password) — the file is not encrypted. It merely carries a flag asking viewers not to allow printing or copying. Compliant readers honour it; free tools strip it in seconds.

People set the second one, see “protected” in the dialog, and believe the document is secure. It isn't. If your PDF opens without prompting you for anything, it has no real protection at all.

2. The password travels with the file

The more common failure, and it has nothing to do with cryptography. You attach the encrypted PDF and type the password in the same email. Anyone who intercepts the message, or who the message is forwarded to, now has both halves. Send the password by a different channel — a text, a call, anything that isn't the thread carrying the file.

And plan for what happens next: your recipient will lose it. A PDF password can't be reset, rotated, or revoked. If it leaks, your only option is to re-encrypt the document with a new password and re-send it to everyone.

When a link password is the better tool

Encrypting the file protects the file, everywhere it goes, forever. That's exactly right for an archive, a document crossing an untrusted network, or anything with a compliance requirement attached.

It's often the wrong tool for sharing, though, because the protection is welded to a copy you no longer control. Putting the password on the link instead keeps the controls in your hands:

We covered that route in detail in how to password-protect a file you share by link. And the two aren't exclusive — for something genuinely sensitive, encrypt the file and put it behind a password-protected link with an expiry date, so a leaked copy is still encrypted and the link stops working regardless.

Quick answers

Related guides

• How to share files securely by link — and what “secure” really means.
• Share a PDF people can view but not download
• Send a file that self-destructs after it's opened