Insert a watermark
In Word for the web, you can see watermarks that are already in a document, but you can’t change them or insert new ones. If you have the Word desktop application, use the Open in Word command to open the document and insert or change a watermark there. When you’re done and you save the document, it will continue to be stored where you opened it in Word for the web.
Use a custom watermark - support.microsoft.com
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.