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Protect PDF

Add a password and AES-256 encryption to a PDF.

Runs entirely in your browser — nothing is uploaded

Drop your PDF here

or click to browse · .pdf

The encryption engine runs in your browser as WebAssembly. Your document and your password are never transmitted — there is no server here that could receive either.

What to expect

  • Encryption is AES-256, the strongest the PDF format defines.
  • The password is required to open the document. Lose it and the file is unrecoverable.
  • Print and copy restrictions are advisory — they depend on the reader choosing to honour them.

Frequently asked questions

Is this real encryption?

Yes. The document’s content streams and strings are encrypted with AES-256 using a key derived from your password. A reader without the password cannot display the file — this is not a flag that asks politely to be respected.

What happens if I forget the password?

The document cannot be opened. There is no recovery, no backdoor and no reset — that is what makes the encryption worth anything. Store the password before you close this page.

Are the print and copy restrictions enforced?

No, and no PDF tool can make them so. Permission flags are recorded in the document and honoured by well-behaved readers, but a reader that ignores them can still print or copy. Only the open-password is cryptographically enforced. This is a property of the PDF format, not a limitation here.

Does my password get sent anywhere?

No. The password is used to derive an encryption key inside your browser and never leaves this page. You can check with your browser’s network panel, or simply disconnect from the internet and watch the tool still work.

Can I encrypt a PDF that is already protected?

Not directly — the existing password has to come off first. Use Unlock PDF with the current password, then protect the result with the new one.

Which readers can open the result?

AES-256 encryption is defined by PDF 2.0 and supported by Acrobat, Preview, Chrome, Firefox and every current mainstream reader. Very old software may not open it.

Password-protect a PDF without uploading it

The documents people most want to encrypt are the ones they least want to hand to a stranger: contracts, medical letters, bank statements, anything with an identity number in it. There is an obvious problem with uploading such a file to a website in order to secure it — for the whole time it is in transit and on that server, it is not secure at all, and you have no way to verify what happened to it.

This tool avoids the question entirely. The encryption engine is qpdf, a long-standing open-source PDF library, compiled to WebAssembly and running inside your browser. Your file is read into memory on your own device, encrypted there, and written back out. Nothing is transmitted.

What the password actually protects

PDF defines two different things that both get called “protection”, and the difference matters.

The open password is real cryptography. The document's content is encrypted with AES-256 and the key is derived from your password. Without it there is nothing to display — a reader cannot show you the document because it cannot decrypt it.

Permissions — the print and copy restrictions — are not. They are recorded in the file as flags, and a reader is expected to honour them. Most do. Some do not, and nothing in the format compels them to. Any tool implying that “disable printing” is enforced is overstating what PDF can do. Treat those settings as a clear statement of intent to a cooperative reader, and the open password as the actual control.

Choosing a password

AES-256 is not the weak point; your password is. A four-character password on a 256-bit cipher is a four-character password. Length does more work than complexity — a passphrase of several unrelated words beats a short string of substituted characters, and is easier to type on a phone.

Whatever you choose, record it somewhere before you close this tab. There is no recovery path, by design. Secure Password Generator will produce one and it, too, runs entirely on your device.

Related tools

To take a password off a document you can already open, use Unlock PDF. To mark a document visually rather than encrypt it, use Watermark PDF. To sign it, use Sign PDF.

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