The two best e-book formats for Kindle are ePUB and MOBI, which are also the two most common e-book formats. Out of these two, MOBI is considered the preferred format for e-books on Kindle Fire. In fact, if you want to download e-books on the Kindle Browser, you will notice that the majority of e-books have MOBI formats. When you download e-books from the Kindle Browser, you will find them in the “Docs” app. Apart from ePUB and MOBI files, Kindle Fire also accepts AZW (.azw3) and KF8 formats. For documents, TXT, PDF, PRC, DOC, and DOCX are also acceptable.