How to password-protect a PDF
- Add the PDFs you want to lock. You can protect several at once with the same password.
- Choose a password and type it twice. Length matters far more than symbols — a short phrase of several words beats a mangled single word.
- Optionally restrict printing or copying text out.
- Press Protect PDF. Encryption happens on your device, so neither the file nor the password is ever transmitted.
About this tool
Password-protecting a PDF encrypts its contents so that opening it requires the password. This free tool applies AES-256 encryption — the same standard used for full-disk encryption — entirely inside your browser.
The privacy argument here is close to absurd when you look at how the alternatives work. A typical online "protect PDF" service asks you to upload the document you consider sensitive enough to encrypt, along with the password you intend to protect it with, so that a stranger's server can put the two together. Whatever the intentions, for a moment both halves of the secret exist on someone else's machine. SiriTools runs the qpdf encryption engine compiled to WebAssembly, in the tab, so both halves stay on your computer.
Two things worth knowing. First, the password cannot be recovered — not by us, not by anyone. There is no reset, because there is no account and no copy. Write it down somewhere safe before you close the tab. Second, the printing and copying restrictions are enforced by the reader, not by mathematics: a compliant reader honours them, and a determined person with the right software can bypass them. The password required to open the file is the part backed by real encryption, and that part is genuinely strong.
Frequently asked questions
- What encryption is used?
- AES-256, applied by qpdf running as WebAssembly in your browser. It is the strongest encryption the PDF specification defines.
- Can you recover my password if I forget it?
- No. Nothing is stored anywhere — not the file, not the password. A forgotten password means the file cannot be opened. Keep a copy somewhere safe.
- Is my password sent over the internet?
- No. Both the file and the password stay in your browser. Nothing about this operation involves a network request.
- What is the difference between a password and the printing restriction?
- The password is real encryption: without it the contents cannot be read. Printing and copying restrictions are instructions to the reader, which well-behaved software honours and specialist tools can ignore.
- Can I protect several files at once?
- Yes. Add them all and they are encrypted with the same password, arriving together as a ZIP.