A watermark is a picture or some text (a company logo, for example) that sits "behind" the main text. It appears on every printed page as if it were part of the paper. You can create a picture watermark or a text watermark, but you can’t have both on the same page.
On the Page Layout tab, click the Watermark button, and choose the watermark you want from the gallery that appears.
If none of the existing watermarks is what you want, choose Custom Watermark from the gallery to display the Printed Watermark dialog box.
To create a text watermark, select Text Watermark, type the text, choose your formatting options, and click OK.
To create a picture watermark, select Picture Watermark, locate and select the picture file you want to use, choose your formatting options, and click OK.
If you decide you don’t want a watermark after all, click the Watermark button on the Page Layout tab, and choose Remove Watermark from the gallery.