Apply Watermark. How to add a watermark to a Word document in Microsoft Office | Microsoft Support Watermarking your own Word files — Office 365 You can easily add a watermark to your own Word files. Go to Pages > Watermark and click the watermark button to add the watermark to each page. If you want to apply watermark to all documents in the project, select both the Watermark group and the Page Layout group and click the Apply Watermark button.