Two passwords: one to open, one for permissions
The password to open is the one everybody needs. Without it, a PDF reader shows a password prompt and nothing of the document. The permissions password, called the owner password in PDF terms, is for whoever may change the restrictions later. According to the qpdf manual, either password unlocks the encryption key, so the permissions password also opens the file. Give it only to people who may change the document.
If you keep printing, copying and editing allowed and leave the permissions password empty, this tool uses your password to open for both. Once you block something, it asks for a separate permissions password. The reason: with 256-bit encryption, a file whose permissions password is empty can be opened without any password at all, which the qpdf command line manual calls insecure.
What restricting printing, copying and editing does
The three boxes set permission flags in the file. A reader that honors them blocks printing, copying text and images, or changes such as editing pages, adding comments and filling in form fields. The qpdf manual is clear that these restrictions are enforced only by the reader software, so a program that ignores them can still print or copy. Treat them as a polite request, good for keeping honest people from editing a contract by accident.
The password to open is real protection: a reader needs it, or the permissions password, to get the key that decrypts the content. If the document must stay private, the password to open is the part that counts, so make it long and do not reuse it. To stamp a document instead, for example as DRAFT, use Watermark PDF before you protect it, and to sign it, use Sign PDF first, since protecting writes a new file.
AES-256, the encryption of PDF 2.0
This tool always uses 256-bit AES. PDF 2.0, the ISO 32000-2 standard and successor of PDF 1.7, deprecates weak encryption and encourages only AES-256, as the Library of Congress format description sums up. The qpdf manual adds that the method was first introduced as an extension of PDF 1.7, and that its revision 6, which this tool writes, is the only one PDF 2.0 does not deprecate. Older PDF encryption with 40-bit or 128-bit keys is not offered here. A PDF reader needs to support AES-256 to open the file, so check it once on the device of the person you send it to.
The work is done by qpdf, an open-source PDF library, compiled to WebAssembly so it runs inside your browser. After writing the file, the tool opens it again to check that it really asks for a password and has the permissions you picked. Only then does the download button appear.
How to password protect a PDF
- 1Drop the PDF on the box. A PDF that already has a password or restrictions has to be unlocked with Unlock PDF first.
- 2Type the password to open twice. To restrict printing, copying or editing, untick it and set a different permissions password.
- 3Press Protect PDF to encrypt and lock the file, then download the copy. Open it once to see that it asks for your password.
Frequently asked questions
Is my PDF or my password uploaded?
No. The encryption runs in your browser with qpdf, an open-source PDF library compiled to WebAssembly. The engine file (about 1.3 MB) is downloaded from this site the first time you use the tool. Your PDF and your passwords are never sent anywhere, not stored and not put into the page address.
What if I forget the password?
This page does not keep your password, so it cannot give it back to you, and Unlock PDF only works when you type the correct one. Keep your original file without a password somewhere safe, or store the password in a password manager.
Can people still print or copy if I block it?
A PDF reader that honors the restrictions blocks those actions. The qpdf manual points out that restrictions are enforced only by the reader software, so a program that ignores them can still print or copy. The password to open is different: a reader needs it, or the permissions password, to get the key that decrypts the content.
Why does it ask for a permissions password when I block printing?
With 256-bit encryption, a file with a password to open and an empty permissions password can be opened without any password, so the restrictions would protect nothing. The qpdf manual describes this, and qpdf refuses to write such a file unless forced. Pick a permissions password that differs from the password to open.
Will the protected PDF open in other programs?
It needs a PDF reader that supports 256-bit AES encryption. According to the qpdf manual, this method came as an extension of PDF 1.7 and is the encryption system of the PDF 2.0 standard, ISO 32000-2. A reader too old to know it cannot open the file.
Can I protect a PDF that already has a password?
Remove the old protection first with Unlock PDF, using the current password, then protect that copy here with the password you want.