An electronic book (variously: e-book, eBook, ebook, digital book, or even e-edition) is a book-length publication in digital form, consisting of text, images, or both, and produced on, published through, and readable on computers or other electronic devices. Sometimes the equivalent of a conventional printed book, e-books can also be born digital.
People can just create an E-book using Adobe software and publish it. I was searching years ago info about how to publish my E-book and among all resources I found, http://createaebook.com/ was the best.
So, if you are interested about anything related to E-books, make sure you check them out!