Add a password to a PDF, without sending it anywhere

There is something genuinely odd about uploading a confidential file to a website in order to make it confidential. The whole point of the exercise is that the document shouldn't be seen by third parties, and the first thing every online tool does is take a copy.

Here the encryption happens in your browser with AES-256, in the form Acrobat 9 introduced (PDF extension level 3). Newer PDF 2.0 files use a slower password check that this tool doesn't write, so choose a long password. Neither the document nor the password is transmitted, because there's nowhere to transmit them to.

You can set the password needed to open the document, and separately restrict what someone can do once it's open — printing, copying text, or making further changes. The restrictions are tied to a separate owner password: type your own, or leave it blank and we use a random one we never keep, so the open password can't lift them. It's worth knowing that those permission restrictions are advisory in the PDF format: compliant readers honour them, but they aren't enforced by encryption and plenty of software ignores them entirely.

What this does — and what it doesn't

  • PDF password protection is a weak control. It keeps casual readers out; it will not stop anyone determined, and password-removal tools are widely available. For genuinely sensitive material, encrypt the file itself or use a secure transfer method.
  • If you forget the password, the document cannot be recovered. We have no copy of either.

Next steps

Unlock PDF

Take the password off a PDF you can already open.

Sign PDF

Draw, type, or upload a signature and place it on any page.

Flatten PDF

Make filled fields and comments permanent, non-editable content.

Edit PDF Metadata

Change the title and author, or strip metadata before sharing.

Protect PDF — frequently asked questions

How strong is the encryption?
AES-256 in the Acrobat 9 form (revision 5). It is not the newer PDF 2.0 form (revision 6), whose password check is harder to guess at, so a long password matters. Permission settings are advisory and ignored by some viewers.
Is my password sent anywhere?
No. The encryption runs in your browser. There's no server involved at any point, so there's nothing to intercept and nothing stored.
What happens if I forget it?
The file can't be opened, and we can't help — we never had the document or the password. Store it somewhere safe before you close the tab.
Can I process many PDFs at once?
Yes. Switch on "Process many files" to give up to 60 PDFs (300 MB in total) the same password and permissions and download a ZIP. A file that already has an open password asks for its own password first, and the new password replaces it. Remember the password: we keep no copy.
Is my PDF uploaded anywhere?
No. Every operation runs in your browser using JavaScript and WebAssembly — the file never leaves your device. You can verify it: load the page, disconnect from the internet, and the tool still works. There is no upload endpoint to send it to.

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