To change the background on all slides in a presentation at the same time–which was very easy in previous versions–Help says choose View–Master slide, then choose Format–Page. There is no Format–Page. What do I do?
Both suggestions are done while in View>Master Slide
Simple background
Simple background here means a built-in background, not a user-image.
Display the style side-pane and click on the Presentation Styles toolbar button (icon at right). Right-click on Background style and Modify. A dialog about Area opens. Choose your background. If you intend ot insert a user-image, select None.
Background image
Make sure no element of the slide is currently selected (e.g. click in a blank area). Insert>Image. While the image is selected, Format>Arrange>Send to Back.
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