Password protecting a PDF encrypts its contents, so the file can't be opened, read or previewed without the password. It is the simplest way to send a payslip, a medical report, a signed contract or a tax document through email or cloud storage without worrying about who else might open it. Here's how to add a password to a PDF, how to choose and share that password safely, and how to remove it again when you no longer need it.
Two kinds of PDF password
- Open password (sometimes called the user password): the file is encrypted and nobody can view it without the password. This is the one that actually protects your document.
- Permissions password (the owner password): the file opens freely, but printing, copying or editing is restricted. Many PDF programs don't enforce these restrictions, so treat them as a polite request rather than real security.
Encryption strength matters too. Modern PDFs use AES with a 256-bit key, which is effectively unbreakable with a good password. Very old PDF tools used RC4 with 40-bit keys, which can be cracked in minutes, so avoid software that still produces them.
How to password protect a PDF for free
- Open the Protect PDF tool.
- Add your PDF by dragging it onto the page or choosing it from your device.
- Type a password, then type it again to confirm.
- Press Protect PDF and download the encrypted file.
How it works behind the scenes: encryption is one of the few jobs Quickaboo does on its server rather than in your browser. The file travels over an encrypted HTTPS connection and is locked with AES-256 by qpdf, a widely used open-source PDF tool. Your original upload is deleted as soon as it has been encrypted, and the protected copy is deleted once you download it, or automatically within 24 hours if you never do.
There is no "forgot password" for an encrypted PDF. If you lose the password, nobody can recover the document, including us. Keep an unprotected copy somewhere safe, or store the password in a password manager.
Other ways to add a password
Microsoft Word (Windows)
If the document starts life in Word, choose File > Save As, pick PDF as the file type, click Options, and tick Encrypt the document with a password.
Preview (Mac)
Open the PDF in Preview, choose File > Export, and use the encryption option (in recent versions of macOS it is under Permissions) to require a password to open the document.
Choosing a strong password
An encrypted PDF can be attacked offline: someone who has the file can try billions of guesses without any lockout. That makes the password itself the whole defence.
- Use at least 12 to 16 random characters, or a passphrase of 4 to 5 random words.
- Don't use names, dates of birth, phone numbers or anything written in the document itself.
- Don't reuse a password from your email or bank.
Our Free Password Generator creates random passwords and passphrases in your browser, and our guide on how long a password should be explains the numbers behind these recommendations.
How to share the password safely
Never send the password in the same email as the PDF. If that one email is forwarded or the mailbox is compromised, the protection is gone. Send the password through a different channel: a text message, a phone call, or a messaging app. For documents you send regularly to the same person, agree a password once in person.
How to remove a password from a PDF
Once a document no longer needs protection, for example before archiving it or merging it with other files, you can remove the password as long as you know it:
- Open Unlock PDF and add the protected file.
- Enter the password. It is checked in your browser first, so a typo is caught instantly.
- Press Unlock PDF and download the unencrypted copy.
Unlock PDF removes a password you already know. It does not crack unknown passwords, and you should only unlock documents you have the right to open.
What password protection doesn't do
Encryption protects the file while it's stored or sent. Once the right person opens it, they can save an unprotected copy, print it or take screenshots. For documents where that matters, add a visible watermark such as "Confidential: prepared for J. Smith" so any copies can be traced back.
Frequently asked questions
Can a password-protected PDF be hacked?
With AES-256 and a long, random password, guessing the password is impractical. Weak, short or common passwords, however, can be cracked quickly with specialist software.
What if I forget the password?
It can't be recovered or reset. Keep an unprotected original somewhere safe, or store the password in a password manager.
Can I password protect a PDF on iPhone or Android?
Yes. The Protect PDF tool works in Safari and Chrome on phones; pick the file from Files or your Downloads folder.
Why won't the tool protect my PDF?
If the PDF already has a password, it can't be encrypted a second time. Unlock it first, then protect it with the new password.