How to Password-Protect a PDF With AES-256 Encryption, in Your Browser
You're emailing your tax documents to an accountant, or a payslip to a landlord, and email isn't exactly a vault. Mail gets forwarded, sits in shared inboxes and lingers in backups for years. Adding a password means that anyone who stumbles on the attachment later still can't open it. Protect PDF does that in the browser.
What you get
The download is encrypted with AES-256, the strongest encryption the PDF standard offers, and it opens in current versions of Acrobat, macOS Preview, Chrome, Edge and most other PDF readers. The encryption is done by qpdf, a well-known PDF tool, compiled to WebAssembly and running in your tab. Before offering the download, the page checks that the new copy really refuses to open without the password, a small step that catches mistakes.
Steps
- Open the tool and pick the PDF.
- Type the password twice.
- Optionally tick the box asking PDF apps to block printing, copying and editing.
- Press Protect PDF and save the download.
- Open the protected file once yourself to confirm the password works.
Choosing the password
AES-256 is only as strong as the password guarding it. A date of birth or a pet's name can be guessed by a cracking tool in seconds, encryption or not. A short, odd sentence is both stronger and easier to remember than a jumble of characters: "green kettle on the third floor" beats "Tr0ub4dor".
Then send the password by a different route than the file. If the PDF goes by email, send the password by text message or tell them on a call. Putting both in the same email defeats the point.
If you need random passwords, Password Generator will make one.
About the "block printing and copying" option
Be realistic about this one. The restriction is a flag written into the file asking PDF apps to behave. Acrobat, Preview and most mainstream readers respect it, but some tools ignore it entirely. It discourages casual copying; it doesn't stop someone determined. The open password is the part that actually protects the content.
Common situations
- Sending ID scans (passport, Aadhaar, PAN) to a hotel or agent.
- Sharing salary slips or bank statements with a landlord or loan agent.
- Storing sensitive PDFs in cloud drives, where an extra lock helps if the account is ever compromised.
- Medical reports going to a relative or a new doctor.
Pitfalls
- Forgetting the password. Nobody can recover it for you, including this tool. Store it in a password manager.
- Already-protected PDFs. Remove the old password with Unlock PDF (you'll need to know it), then protect the unlocked copy with the new password.
- Batches. There's no multi-file mode; protect each file in turn with the same password. Each one is checked individually.
Password vs. other ways of sharing
A password-protected PDF is the simplest option that works for everyone: the recipient doesn't need an account, an app or a link that expires. Shared cloud links with access controls are fine too, but they depend on the other person signing in with the right account, and they stop working when someone tidies up a drive. For one-off documents to an accountant, a landlord or a relative, a locked attachment plus a password by text message is hard to beat.
Privacy
The page states the PDF and password stay in the tab and are never uploaded, stored or placed in the address bar. That's how it should be for a tool whose entire job is secrecy. The page carries Google ads, like the rest of the site.
FAQ
What encryption does it use? AES-256.
Can I remove the password later? Yes, with Unlock PDF and the same password.
Is the password sent anywhere? No, the encryption happens in your browser.
Will the recipient need special software? No, any current mainstream PDF reader will ask for the password and open it.
Before the next sensitive attachment goes out, lock it with Protect PDF.
— Alok Kumar Singh