How to password protect a PDF

Password protecting a PDF in PDF by Zaweba is done from Protect, then Protect with a password. You can set a password that's needed to open the file, a permissions password that controls what people may do with it, or both. Encryption is AES 256-bit by default, and a strength meter shows how good your password is. The app is free and works offline on Windows.

Because nothing is uploaded, the document you are protecting never leaves your own computer, which is rather the point.

Open password and permissions password

A PDF can carry two different passwords, and it's worth knowing which you need.

The password to open is the lock on the front door. Without it, the file can't be read at all. Use it for anything private you're emailing or storing on a shared drive: payslips, medical letters, contracts.

The permissions password controls what everyone else may do once the file is open. You choose whether printing is allowed at high quality, low quality or not at all, and whether people may change content, add comments, fill in forms, change pages or copy. Someone without the permissions password can read the document within those limits.

You can set both. A common pairing is an open password you share with the recipient and a permissions password you keep to yourself.

Setting the passwords

Open the document and choose Protect, then Protect with a password. Tick the passwords you want and type them. If you're setting permissions, choose what's allowed. Leave the encryption at AES 256-bit unless you have a reason to change it, then save.

Close the file and open it again to check the password works before you send it.

Choosing the encryption

The choices are AES 256-bit, AES 128-bit, RC4 128-bit and RC4 40-bit. AES 256-bit is the strongest and the default, and almost every modern PDF reader opens it. The older RC4 methods are there for compatibility with very old software and are much weaker; use them only if someone genuinely can't open an AES file.

Choosing a good password

The encryption is only as strong as the password. The strength meter helps here. A long phrase of several unrelated words is both stronger and easier to remember than a short string of symbols.

Send the password a different way from the file. If the PDF goes by email, give the password by phone or text message. Sending both in the same email is like taping the key to the door.

Keep a note of the password somewhere safe. If you lose an open password, the file is properly locked.

Checking and changing protection later

Protect, Security details shows how a file is protected: the method, which password opened it, and each permission. Remove security takes protection off, once you have opened the file with the password.

Remember that permissions depend on the reader respecting them. They stop casual copying and printing, and they're a clear statement of your wishes, but an open password is what actually keeps the contents private.

If you protect files often, Tools, Actions can include a protect step, so a whole folder can be locked in one run. PDF by Zaweba does it all on your own PC.