Multimedia Keynote presentations help you communicate your ideas to an audience. However, the more images, movies and audio effects you employ in your presentation, the larger the size of the file. When you reduce the file size of a Keynote presentation, Keynote eliminates the unused portions of the media, according to the Apple website. Once you reduce the file size, you can't return the images and other media to their original quality.
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Go to the "File" menu and select "Save." Enter a name for the file and a save location.
Open the "File" menu and select "Save As." Add the word "reduced" to the file name and select a save location. This step is optional, but recommended in the event you want to return to the full quality version at a later point.
Go to the "File" menu and select "Reduce File Size." Keynote will calculate the amount of the file size reduction. Press "Reduce" to reduce the Keynote file size.
Open the "File" menu and select "Save" to save the file in the reduced size.