Editing and modifying PDF files requires the use of a PDF editor
Reference software: Swift PDF Editor
Reference steps: 1. Open Swift PDF Editing on the desktop and then open the PDF file in the editor
2. Select "Watermark" - "Manage" in the upper menu bar
3. Then a window for managing watermarks will pop up. , after selecting to add a new file, a window will pop up, and you can modify and edit the PDF file
4. After editing and modifying the PDF file, you can save it