PDF Protect puts an opening gate on a file: without the password, no reader will open the document. The encryption runs in your browser through qpdf's WebAssembly build, with AES-256 — the strongest tier the current PDF standard defines, matching the high-strength setting in Acrobat's password encryption.

It does one job and only one: setting an open password. It does not offer permission restrictions of the “opens, but printing and copying are forbidden” kind.

1. 01Pick the fileclick the PDF you want to encrypt in the list on the left; if it is already encrypted, the page asks you to unlock it before setting a new password.
2. 02Enter the passwordtype at least 4 characters under “Password” and repeat it under “Confirm password”; a mismatch is reported.
3. 03Encrypt and downloadclick “Encrypt and download” to get <original-name>_encrypted.pdf. The original file is left as it is.

Supported input

unencrypted standard PDFs.

What is encrypted

the original file bytes as imported; if you rotated or deleted pages in the page organiser, export the current arrangement first and encrypt the export.

Permissions

the open password and the permissions password are one and the same, so printing, copying and editing are all unrestricted once the file opens; a separate permissions password is not available.

Compatibility

AES-256 requires a reader that supports PDF 1.7 extension level 3 (Acrobat 9 and later, modern browsers, mainstream mobile readers); very old readers may fail to open the file.

What it does not do

it cannot recover a lost password (lose it and the content is gone), does not do certificate encryption, and does not add a watermark (use “PDF Watermark” for that).

Encryption is performed by qpdf (WebAssembly) in the browser; neither the file nor the password is sent to a server.