I still have the troubles that the PDFWatermark didn't work - and now i tried to generate the watermark with an SVG Image, which i will print before the real pdf data.
The output looks good, but because of the pdf engine didn't work with GDI+, i has to convert the SVG into a GDI EMF.
the problem is, that the size of the pdf grows (needing about 280kb instead of 44kb) if i compare the output from coreldraw
the second problem is, that every text is transformed into curves and therefore i can't select the text in the pdf the anymore.