If you are using a theme - Modify the Theme to add the "watermark" style:
Format | Theme | Modify/Customize | Text - select More Text Styles
Select the body tag and then Modify | Border | Shading and select
Repeat - select no-repeat
Attachment - select fixed
Vertical Position - select center
Horizontal Position - select center
OK|OK|OK|OK & Save As a new theme name
--
| how do I create a theme so the background image is watermark?