How to Password Protect a PDF

Locking a PDF the right way

A PDF travels farther than any other document — emailed to a client, shared in a group chat, uploaded to a portal. Once it leaves your hands, you cannot control who opens it. A password is the simplest fix: anyone with the password opens the file normally, anyone without it sees nothing at all. The catch is that many free tools that add a password do it by uploading your file to a server first — which means the document you wanted to keep private just passed through someone else's computer. This tool does the job differently: the password is added in your browser, and the file never leaves your device.

What "protected" actually means here matters. The tool uses AES-256 encryption — the same standard Adobe Acrobat uses — applied with qpdf, an open-source PDF tool. Encryption scrambles the contents of the file so that only the password can unscramble them. It does not change what is inside: the text stays selectable and searchable, the pages keep their size and order, and the file still opens in any PDF reader — it simply asks for the password first. Before handing you the result, the tool verifies its own work: the finished file must refuse to open without the password and must open with it, with the same page count as the original. If that check fails, you get an error instead of a broken file.

To do it, drop a PDF onto the Protect PDF page — up to 20 files at once, 100 MB in total, all with the same password — and type the password twice. The second typing is not bureaucracy: a password you mistype once is a password you can never open the file with again, and there is no way to recover a forgotten password, not here and not anywhere. Pick something you will remember, or store it in a password manager before you press Protect. Press the button and download the encrypted file. If the PDF is already password-protected, unlock it first with the Unlock PDF tool, then protect it with the new password.

A few honest limits. A password protects the file, not the person reading it: anyone you give the password to can open the file, and can also remove the password. It is a lock on the document, not a tracking system. Use a password that is long enough to matter — a single word or a birth year is barely a lock — and do not reuse the password you use for your email. For everyday documents — a contract, a medical report, a payslip, a set of exam papers — a strong password added in the browser is the right level of protection, and it costs nothing. And remember: because the file never leaves your device, there is no copy of your document sitting on a server to be leaked later.

How to use this tool

1. 1Drop a PDF onto the Protect PDF page (up to 20 files, 100 MB in total).
2. 2Type a password, then type it again to confirm.
3. 3Press Protect PDF and wait a moment while the file is encrypted.
4. 4Download the protected file and try opening it — it must ask for the password.
5. 5Store the password somewhere safe; a forgotten password cannot be recovered.