PDF passwords are outside this release
The current Scan to PDF application collects scanned pages or local images and saves a PDF. It does not set, recover or remove PDF passwords, and no registration or paid upgrade enables that absent function.
Create the scanned document first
Scan or import the pages, arrange them and save a new PDF. Keep the original images and a copy of the unmodified document.
Use a tool that explicitly supports PDF security
If your document needs password protection, use a separate PDF application with that stated feature. Protected existing input needs the appropriate password and access before it can be processed.
The current Windows product directory lists the supported free applications. It does not offer an installer for this absent product or function.