What is the difference between MOBI, EPUB, and PDF Ebook?

MOBI, EPUB, and PDF ebook are three different formats for ebooks. MOBI and EPUB ebooks are flowable formats, so text can flow from one page to the next if the font size is changed. PDF ebook is a fixed format, so the text on a particular page will always look exactly the same. MOBI is the format that is used on Amazon Kindles, and EPUB is used on most other ereaders.