How to modify (watermark) existing PDF document

I’ve reviewed the Aspose.pdf.java API and sample code, but can’t see how to modify an existing PDF document. I want to add watermarks to a PDF file created by some other application. Is this possible?

Hi,

Thank you for considering Aspose.

That is supported by another product Aspose.Pdf.Kit.

Please refer to online demo of Aspose.PDF.Kit.

http://www.aspose.com:8081/Products/Aspose.Pdf.Kit/Demos/General/GeneralDemos.jsp.