Included in your e-book purchase are three files: PDF, .epub, and .mobi. To open and read the epub file, we recommend using an e-reader program like the Apple Books app or the Google Play Books app. To open and read the mobi file, we recommend using Amazon’s Kindle app, available for download on a variety of platforms and devices. To learn more about other e-reader programs available, we recommend contacting the maker of your preferred device.