When you publish a book, your goal is to reach as many readers as possible. But for millions of people, your book may not be readable at all—unless you’ve taken steps to make it accessible.

In the world of ebooks, accessibility means making sure your file is usable by everyone, including readers with visual, cognitive or physical impairments. In other words, every book should be accessible to people who use screen readers, text-to-speech software, braille displays, or other assistive technolo...