Protect a PDF with a password

Add interoperable PDF password protection without a server round trip. A local qpdf WebAssembly worker writes standard AES-256 encryption, so the output remains a real PDF rather than a proprietary encrypted archive.

Encryption is AES-256, applied by the qpdf engine, which is the standard mainstream PDF readers expect. A file protected here opens with its password anywhere that opens PDFs, rather than only in the tool that made it.

Choose a password you can send separately. The weak point of a protected PDF is almost never the cipher; it is that the password gets emailed in the same thread as the document, leaving both in one inbox. Sending the file one way and the password another is what makes the protection worth applying at all.

Protection controls opening, not what happens afterwards. Once a recipient has the password they can read, copy, print, and forward the contents, and permission flags that claim otherwise are advisory and widely ignored by readers. If material must not be redistributed, encryption is not the control that achieves it.

A forgotten password cannot be recovered, by us or by anyone else. That is the point of the cipher. Keep the original unencrypted file somewhere safe before protecting the copy you are sending.

The password is typed into a page with nowhere to send it. It is used by a local worker and exists only in memory while the document is written, which is a materially different proposition from uploading a confidential file and its password together.