Fixed-layout ebooks use the EPUB file format or an interactive PDF file to create the ebook. They can also be sold and purchased through third-party retailers, such as Apple’s iBookstore and Amazon. These ebooks feature two-page spreads and page-turn animations in the iPad and Kindle Fire to give you the experience of reading a traditional print book.
PDFs, on the other hand, cannot be purchased through the iBookstore or through Amazon. While a PDF can be saved and viewed on Apple or Kindle devices they don't have the full-display capabilities of a fixed-layout ebook.