PDF. 3. Choose the type from the drop-down menu. · 4. Choose the password or certification. · 5. Click the “Lock” button” in the bottom right corner of the window. How to Password Protect PDF Documents in Windows • Press Ctrl+Alt+Del in combination with a combination of the keyboard's Alt+Enter keys. This will lock the PDF after the cursor is moved to the top of the page How to Password Protect PDFs in macOS 1. Open Adobe Acrobat. • 2. Select ′File…′ in the File menu. • 3. Select ′File A PDF‹ on the menu. • 4. Select ′Protect from the menu. • 5. Enter the password or certification. • 6.