A watermark is used to indicate that a slide is still a draft, contains confidential information, or simply indicate that it should not be used beyond the intended purpose.
Click on the “View” tab which is located in the ribbon of your PowerPoint presentation. click on the “Slide Master” option which is located in the “Master Views” section of the “View” tab.
Click on the “Insert” tab which is located in the ribbon of your PowerPoint presentation.
Click on the “Text Box” button located in the “Text” section of the “Insert” tab and add a text box in the “Master Slide”
Type the text in the text box that you want to keep on the background of your presentation as a watermark and format it to fit your preference.
Click on the individual slide layout of the selected slide, and add the watermark specifically to the slide. Click on “Close Master” to exit the Slide Master.