Changing an e-book into an audio file usually requires the use of digital publishing platforms such as Amazon's Amazon or Apple's iBooks, or online audio publishing platforms such as Spotify or Apple Music. These platforms all provided the option to convert e-books into audio files. On the digital publishing platform or online audio publishing platform, choose the export option and then choose the e-book file to export. Next, the platform would generate an audio file with the same name as the e-book file and contain the same meta-data information such as author, title, and publication date. Save the generated audio file in an audio file archive such as Google Play Music or Apple Music, or on your local computer. You can play the audio content in the e-book by visiting these libraries and selecting the audio file you want to play. It is important to note that different digital publishing platforms or online audio publishing platforms may have different export options and format, so you need to carefully check the platform's help documents for details.