For protected PDFs, the most effective method involves using the browser's to run a script that captures each page as an image and recombines them into a new file.
Downloading locked or view-only files from Google Drive is often necessary when you need offline access to documents or media where the owner has disabled the standard download button. While these restrictions are designed to protect content, several technical workarounds allow you to save local copies of PDFs, videos, and Google Docs. Downloading View-Only PDF Files download locked files from google drive