When to password-protect a PDF
A password keeps a PDF private when it travels through channels you do not control: email, chat apps, cloud folders, USB sticks. Typical examples are payslips, tax documents, medical reports, contracts and scans of ID cards. Without the password, the file cannot be opened at all, even if someone gets a copy of it.
Open password and permissions
A PDF can have two kinds of protection:
- Open password (also called user password). It is needed to open and read the document. The content is encrypted, so without the password the file is unreadable. This is the protection you want for confidential documents.
- Permissions with a permissions password (also called owner password). Turn on Restrict printing, copying and editing and choose what stays allowed: printing (allowed, low quality only, or not allowed), copying text and images, editing content, adding comments, filling in forms, and inserting, rotating or deleting pages. The permissions password lets you change these rules later. If you leave it empty, a random one is used, so nobody can lift the restrictions in Acrobat.
You can use both together: an open password for the people you send the file to, and permissions that limit what they can do with it. The permissions password must be different from the open password; otherwise anyone who can open the file could also lift the restrictions. If the PDF is already protected, its old password is replaced by the new one.
Keep in mind that permissions are a rule that PDF programs are asked to follow. Well-known readers such as Acrobat, Chrome and Preview respect them, but some programs ignore them. Only the open password gives real protection of the content.
How strong is the encryption?
The tool uses AES with a 256-bit key, the strongest encryption that the PDF standard supports. It is built on qpdf, a widely used open-source PDF library. All current PDF readers can open such files: Adobe Acrobat and Reader, Chrome, Edge, Firefox, macOS Preview and the PDF apps on Android and iPhone. If the file must open in a very old reader that cannot handle AES-256, choose AES-128 instead; it is still secure. Before the protected file is offered for download, the tool checks that it really refuses to open without the password and that the permissions are set as you chose.
The encryption is only as strong as the password. Use at least 12 characters, mix words, digits and symbols, and do not use names or dates of birth. Send the password through a different channel than the file, for example by phone or text message if the PDF goes by email.
Do not lose the password
We do not store your password and cannot recover it. A PDF encrypted with a strong open password cannot be opened without it, not by us and not by any other tool. Keep the password in a safe place, such as a password manager, and keep an unprotected copy of important files.
Private by design
Encryption happens inside your browser. The PDF and the password are not sent to our server. To remove the password later, when you no longer need it, use Unlock PDF. To add a visible mark such as CONFIDENTIAL to every page as well, use Add Watermark before you protect the file. If you edit a protected file with other tools here, add the password again at the end.