Zipping a PowerPoint presentation reduces the size of the file, making it easier to transfer the file between computers. The Mac operating system includes an archive utility that can zip files. When you compress a PowerPoint using the ZIP format, the file format changes, so you cannot run it in PowerPoint. To do that, you must unzip it. Unzipping decompresses the file and returns it to the original format.
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Navigate to the PowerPoint presentation in the Finder.
Control-click or right-click on the presentation.
Select "Compress [your_filename]" from the pop-up menu. The .zip file appears in the same folder as the original.