Set a hyperlink base
Open the presentation you want to set a hyperlink base for.
On the File menu, click Properties, and then click the Summary tab.
In the Hyperlink base box, type the path to the files you hyperlink to.
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About hyperlinks and action buttons
In Microsoft PowerPoint, a hyperlink is a connection from a slide to another slide, a custom show, a Web page, or a file. The hyperlink itself can be text or an object such as a picture, graph, shape, or WordArt. An action button is a ready-made button that you can insert into your presentation and define hyperlinks for.
Powerpoint has a HELP function