How to remove a password from a PDF

If you know a PDF's password, removing it takes a few seconds: the file is decrypted with that password and saved as a copy that opens without one. If you don't know it, there is no shortcut, because the password is what unlocks the encryption in the first place. Files that open normally but won't let you print or copy are a third case, and those can be unlocked without typing anything. Unlock PDF handles the first and third cases in your browser, without uploading the document anywhere.

Two kinds of PDF password

PDF encryption can use two different passwords, and they do different jobs:

• Open password (user password). A viewer asks for it before it shows the file at all. Without it, the contents stay encrypted.
• Permissions password (owner password). The file opens normally, but printing, copying text or editing may be blocked. The owner password is what lifts those limits.

The documentation of qpdf, the open-source PDF tool that Unlock PDF runs, explains how the two relate. Both passwords recover the same encryption key: “either password can be used to retrieve the encryption key.” A file can also be encrypted with an empty user password. In that case the empty string unlocks it, so it opens without asking, and only the restrictions remain. qpdf calls this a file that is encrypted but not password-protected, and it's what people usually mean by a “restricted” or “secured” PDF.

How to tell which one you have

You don't have to work this out yourself. When you add a file to Unlock PDF, it checks the file first and tells you which case it is: the PDF needs its password to open, it opens without a password but blocks printing or copying, or it has no password or restrictions at all. It asks for a password only in the first case.

Remove a password you know

1. Open Unlock PDF and choose the file.
2. If it asks for the password, type the one you'd use to open the file in a viewer. If you were given the owner password instead, that works too, since either one recovers the key.
3. Select Unlock PDF and save the copy. Its name ends in -unlocked, so it's easy to tell apart from the original.

The pages are kept exactly as they are; only the encryption is removed. If the password is wrong, you'll see a message that it doesn't open this PDF, and nothing is saved. Your original file isn't changed either way.

Common reasons to do this:

• Statements and payslips. Some banks, card issuers and employers send statements as encrypted PDFs, and typing the password every time you open an old one gets tedious.
• Combining or converting files. Tools such as Merge PDF, Split PDF and PDF to JPG can't open a file that needs a password, so you unlock it first.
• Your own old files. Documents you protected years ago and now want to archive or share in a different way.

PDFs that block printing or copying

If a PDF opens without a password but won't print, or won't let you select text, it carries restrictions tied to an owner password. Unlock PDF removes them without asking for anything, because the file can already be decrypted with the empty user password.

It helps to know how thin this protection is. qpdf's documentation says the restrictions placed on PDF files are “solely enforced by the software,” and that there is “fundamentally no way to prevent an application from disregarding the security restrictions on a file.” A restriction is an instruction that well-behaved viewers follow, not a lock.

That has two consequences. If you want to keep a document private, rely on an open password, not on restrictions. And lift restrictions only on files you have the right to change. qpdf's own documentation says its decrypt option is not intended for bypassing copyright restrictions or other restrictions that producers place on files, and the same goes for this tool. A publisher, employer or school may have set them for a reason.

Why a forgotten open password can't be removed

An open password isn't a sticker on top of a readable file. The contents are encrypted, and the password is needed to recover the key that decrypts them. Without it, a viewer has only scrambled data to work with, and so does any converter or unlocking tool. With modern AES-256 encryption, qpdf's documentation adds that there is no way to recover the user password from the owner password, either.

Unlock PDF never guesses or tries passwords. If you don't know the open password, it can't unlock the file, in the same way a PDF viewer can't open it. What you can do instead:

• Look through the email or letter that came with the file. That's where a sender would explain the password or how it's formed.
• Ask the sender for the password, or for a copy without one.
• If it's a file you protected yourself, look for the unprotected original.

A password-recovery service can only guess, and to do that you would be handing your document to someone else.

After unlocking: keep the copy safe

An unlocked copy opens for anyone who gets hold of it. Keep it somewhere private, delete it when you no longer need it, and don't forward it in place of the protected original.

If you need to lock it again, for example after merging several statements into one file, use Protect PDF. It encrypts the file with AES-256 and an open password you choose, with an option to also block printing and copying. Write the new password down: nobody, including Inplace, can recover it for you. Changing a password works the same way: unlock the file with the current password, then protect the result with a new one.

Why unlock in the browser

The PDFs people need to unlock are usually the sensitive ones: bank statements, payslips, tax forms, medical letters. Many online tools upload the file, and sometimes the password, to their server. Unlock PDF runs qpdf compiled to WebAssembly inside your browser tab, so the document and the password stay on your device and aren't stored anywhere.

Sources

• qpdf documentation: PDF encryption (user and owner passwords, security restrictions)
• qpdf documentation: Running qpdf (--decrypt and --password)