We're releasing our Artek-Utilities module for free! It includes Apache PDFBox to perform various pdf manipulations (merging, splitting, add watermark, etc).
You can download it here: Community | Artek Integrated Solutions
For a useable preview check out our demo project: Perspective
The project will be hosted on the exchange as well for sample code.
We're open to feedback and expanding the functionality- feel free to reach out to us at info@artekis.io