Password-protect a PDF with AES encryption
Add a password to a PDF so it can't be opened without it, using 256-bit AES — the same encryption commercial PDF software applies. The document is encrypted inside your browser tab, which means the file and the password you choose are never uploaded to anyone. Send the protected file however you like, and share the password through a different channel.
How to password-protect a PDF
Add the PDF
Drop in the document you want to protect.
Set a password
Choose a strong open password. There's no recovery — if it's lost, so is the document, so store it somewhere safe first.
Encrypt and download
Press Protect. The encrypted PDF is written locally and downloaded, and will prompt for the password on every open.
What Protect PDF can do
256-bit AES
Real encryption, the same standard desktop PDF software uses.
Password never uploaded
Encryption happens in the tab, so nothing you type reaches a server.
Opens everywhere
Standard PDF encryption — Acrobat, Preview, Chrome and mobile readers all prompt correctly.
Free and unlimited
No account, no per-document cost, no file-size ceiling.
Protect PDF — frequently asked questions
How strong is the encryption?
AES-256, which is the strongest option the PDF specification defines. The real weak point is the password you choose, so make it long.
What happens if I forget the password?
The document is unrecoverable. There is no back door and no reset — nobody, including us, holds a copy of the key. Write it down before you close the tab.
Can I stop people printing or copying text?
Permission flags are set alongside the password. Treat them as a deterrent rather than a guarantee: some readers honour them and some don't.
Do my PDFs get uploaded to a server?
No. Every tool on Notoo Tools runs as JavaScript and WebAssembly inside your browser tab. There is no server that receives your files — you can disconnect from the network after the page loads and the tool keeps working.
Do I need an account or a subscription?
Neither. There's no sign-up, no email, no free-tier limit and no watermark. Bookmark the tool and it opens straight into the work.