KelpMark helps creating watermarks on images or PDFs.
Suppose you have your passport: 
And need to send it to some company, but don't trust them because they might have security breaches and might leak your data. So you want to watermark it to make it harder to reuse in case of data leak.
Then you can save the resulting image/PDF: 
- Import multiple images at once
- Import multi-page PDF
- Export to single image
- Export to multi-page PDF
- Watermark text tiling
- Various graphical features
- PyQt5
- python-poppler-qt5
KelpMark is licensed under the Unlicense.