MOBI & EPUB eBook Files
An eBook is a very different format than a print book. While a print book can be digitized by creating a PDF, a PDF is not the same as an eBook.
Just because something can be viewed on a computer doesn't mean it will work on everything electronic. A PDF can't just be scanned and then viewed on the Kindle.
A true eBook has one of two file types: MOBI or EPUB. Essentially, the only difference between these is the accessibility. MOBI can only be read on the Amazon Kindle. EPUB is the "universal" file type that can be read on everything else.
If you’re planning on publishing your book as an eBook, you’re going to want to make sure that you get both of these file types. It takes a special process to create MOBI and EPUB files, and it’s recommended that you do some research before deciding to do it on your own.