Use a custom watermark - Microsoft Support
support.microsoft.com › en-us › officeFirst, create your custom watermark. On the Design tab, select Watermark > Custom Watermark. Choose Picture Watermark and select a picture, or choose Text watermark and type your watermark text in the Text box. Click OK. Next, save the watermark so you can use it in other documents. Double-click near the top of the page, to open the header.