I wanted to add a watermark at background of the diagram control and this is depending on the user preference to have the watermark. The watermark(mostly words) should appear in the background.
Does goXam diagram control has any feature to do this ?
There are several ways to do that, depending on the effect that you want. There is discusiion about this in the GoXamIntro.pdf document in the section about “Decorative Elements and Unbound Nodes”.
If I were you I would probably choose the first way, adding an XAML element behind the Diagram, which would have a transparent background.