How to Password Protect a PDF (and Remove a Password You Know)

Emailing a payslip, a medical report or a contract as an ordinary PDF means anyone who gets hold of the email (or the device it's stored on) can open it. A password adds a strong lock. Here's how to add one properly, and how to remove it again when you need to.

Two kinds of PDF password

PDFs support two separate passwords:

• Open password (user password): needed to open and read the document. This is real protection: without it, the contents are encrypted and unreadable.
• Permissions password (owner password): restricts printing, copying text or editing. These restrictions are respected by most PDF programs, but they're a polite request rather than strong protection; some software ignores them.

For confidential documents, the open password is what matters.

Protect a PDF

1. Open Protect PDF and add your file.
2. Enter a password. Use at least 10 characters, ideally a passphrase of several random words.
3. Optionally restrict printing, copying and editing.
4. Download the protected PDF.

The file is encrypted with AES-256, a modern standard. With a long password it can't realistically be broken by guessing. Short, simple passwords, though, can be guessed by software, so length matters more than anything.

Need a good password? The Password Generator creates strong random passwords and passphrases.

Share the password separately

The most common mistake is sending the password in the same email as the PDF. If the email is intercepted or forwarded, both arrive together. Instead:

• Send the PDF by email and the password by text message or phone call.
• Or agree on a password format in advance.

Remove a password you know

Typing the password every time gets tiresome for your own files. To remove it:

1. Open Unlock PDF and add the protected file.
2. Enter the password.
3. Download an unlocked copy that opens without asking.

This only works if you know the password. It's not a password-cracking tool. If you've forgotten a password, the only options are to ask the person who set it or find an unprotected original.

You'll also need to unlock a PDF before some edits, such as compressing, merging or converting it.

Don't lose the password

There's no "forgot password" for an encrypted PDF. If you lose the password and don't have an unprotected copy, the contents are gone. Store passwords in a password manager, and keep an unprotected original somewhere safe if appropriate.

Common questions

Will the recipient need special software? No. Every common PDF reader, including the ones built into browsers and phones, asks for the password and opens AES-256 encrypted PDFs.

Can I protect a PDF so it can be read but not printed? Yes, with the permission restrictions. Remember they're respected by most programs but aren't strong protection; someone determined could take screenshots or use software that ignores them.

Does protecting a PDF make it bigger? Barely. Encryption doesn't add much to the size.

Can I change the password? Unlock the PDF with the old password, then protect it again with the new one.

Your password never leaves your device

Encrypting a document by uploading it, along with its password, to someone else's server rather defeats the purpose. Here, both encryption and decryption happen in your browser. Neither the file nor the password is sent anywhere.

Summary

• Use an open password for real protection, at least 10 characters.
• AES-256 is strong; weak passwords are the weak point.
• Send the password through a different channel.
• Unlock only files whose password you know.