An ebook is more than an electronic version of your book—it's your book converted into a file format suited for an ereader or electronic device. This format is different from the Word document or PDF file of your manuscript.
Whereas you might use Microsoft Word to write and edit, then have your book interior designer create a PDF for your print book, ebooks are designed to be flexible; readers can change the font size, line spacing, and even the margins of their ereader display. For an ebook to adapt to this kind of flexibility, it must be specially coded, much like a website would be.
The short answer, then, is that print books and their PDF counterparts are rigid and fixed in their formatting, and ebooks are made to be flexible and adapt to the user’s specifications. The picture below is an example of how an ebook’s appearance can be changed on an ereader.
