If your document has a watermark and you want to remove it from every page, you can.
Click Design > Watermark.
In the Insert Watermark box, select No watermark.
If that doesn’t work, the watermark might have been applied to only a specific section of the document.
Remove a watermark from a section
Even though watermarks don't show up in the header area, Word anchors them to headers. So, to remove a watermark that was applied to a section, you'll need to access it from the header area.
Double-click to open the header area of any page the watermark is on.
Click the watermark to select it, and press Delete.