PowerPoint documents. Add a watermark · Select the Slide Master. · Click Add Image. · Select an image from the images in your slide deck. Use the watermark as the color of the slide. How to Use Watermarks in PowerPoint — Microsoft Answers Nov 28, 2022 — It's not quite as easy to add watermarks to. For this, the watermark text need be “textured out” to slide it over the surface of the slide, which is achieved by filling with some kind of dark or light background color or brightening on color to achieve the desired effect.