Modufile's Protect PDF tool adds AES-256 encryption and password protection to your PDF files directly in your browser. You can set a user password (required to open and view the document) and an owner password (required to change permissions such as printing, copying, and editing). All encryption is performed client-side using the MuPDF engine compiled to WebAssembly — your files and passwords are never sent to any server. AES-256 is the strongest encryption standard supported by the PDF specification and is the same level used by financial and government institutions.