How to password-protect a PDF
A password stops anyone without it from opening your PDF. Here’s how to add one properly, and how to share the password without undoing the point.
If you email a payslip, a medical report or a contract, it can end up in more inboxes than you intended through forwarding, a wrong address, or a hacked account. A password on the PDF means the file is useless to anyone who doesn’t also have the password.
How to add a password
- Open Protect PDF and add your file.
- Type a password, then type it again to confirm.
- Choose whether people with the password can print, copy text, or edit.
- Select Protect PDF and download the locked copy.
Open the locked file once to check the password works before you send it. Keep your unprotected original somewhere safe: if you forget the password, there’s no way to recover it.
What the protection actually does
UserPDF uses AES-256, the strongest encryption in the PDF standard. Without the password, the contents of the file are scrambled; it isn’t just hidden behind a prompt. A long, unguessable password makes the file practically impossible to open without it.
The print, copy and edit restrictions are different. They’re instructions that PDF readers are expected to follow, and most do, but some software ignores them. Treat them as a polite request. The password is what keeps the file private.
Choosing a good password
- Longer beats complicated. Three or four unrelated words, like harbour-violet-tractor-71, are stronger and easier to type than a short jumble of symbols.
- Don’t reuse a password from an email or bank account.
- Avoid things people can find out, such as birthdays, pet names or the recipient’s name.
Sharing the password safely
The most common mistake is sending the password in the same email as the file. If that email goes astray, both arrive together and the protection does nothing.
- Send the password by a different route: a text message, a phone call, or a messaging app.
- For a regular contact, agree a password once in person or by phone and reuse it for that relationship.
Removing a password later
If you need an unlocked copy of a PDF you have the password for, use Unlock PDF. It removes the password and any restrictions so the file opens normally. It can’t help with a forgotten password; nothing can, which is the point of good encryption.
More guides
- How to make a PDF small enough to emailMost email services won’t send attachments over about 20–25 MB. Here’s how to get a PDF under the limit without wrecking it.
- Are online PDF tools safe to use?Most online PDF tools upload your file to a company’s server. Here’s what that means, and how to choose a tool you can trust with private documents.
- How to sign a PDF without printing itPrint, sign, scan, email: there’s a faster way. Here’s how to sign a PDF on your computer or phone, and when an electronic signature is enough.
- How to fill in a PDF form on your computer or phoneSome PDF forms let you type straight into them; others are just pictures of paper. Here’s how to fill in both kinds.