If you would like to have watemark in the PDF document.
1. Create PDF Setup document
Select "View - Go to..." - "PDF setup documents" view
Create new document (i.e. "# TEST Watermark") and in the Watermark tab set Print watermark to yes.
2. Setup the Office document to the PDF watermark creation
In the Office document you should set "SW_PDFWatermarkText" custom document property to your sign.
Or:
programatically set "SW_PDFWatermarkText" custom document property before the PDF creation start.