There's more to choosing a format for your e-book than PDFs versus executable files (.exe files). Here are a few of the e-book formatting decisions you'll have to consider when writing an e-book:
- Do you want your e-book to be in a program file of its own (.exe file) or PDF, or another format altogether?
- Do you plan to protect your e-book (from copying, printing, etc.), and if so, how?
- What size font do you want to use? I'd recommend no larger than 14pt, but that can be pushing it in some cases (depending on the font).
- What font do you want to use? (Tip: Sans serif fonts are generally easier to read on-screen, and serif fonts are easier to read in print. When choosing, think about your audience, the length, etc. and determine whether it's more likely to be read on-screen or printed out.)
- How long do you want your e-book to be? You can't choose an exact page number, but at least come up with an estimate. Are you planning a short e-book of 20-30 pages, something more traditionally book-length, etc.?
- How do you plan to visually break the e-book up? E-books should have some kind of visual element to prevent them from becoming page after page of nothing but straight text. Your topic may lend itself well to charts and graphs. If it's tutorial-based about something done on the computer, screenshots can be a good graphical element. You can also use asides for additional text (break them off with boxes or in other ways, treating them as image elements).
- Do you plan to embellish the overall look of the e-book (page borders, colored sub-headings, etc.)?
It's a good idea to look at all of your options based on what you think your own target readers would most appreciate. There's no right or wrong here, and the end results are going to vary quite a bit from e-book to e-book.