Your finished manuscript is just the beginning. To publish on Amazon, that text needs to be packaged into a specific file format. The two most common you'll encounter are EPUB and KPF. The EPUB format is the industry standard for e-books. It's an open format, meaning it isn't controlled by any single company. If you plan to sell your book on multiple platforms beyond Amazon, a process known as 'wide distribution', you'll almost certainly use an EPUB file. KPF, or Kindle Package Format, is Amazon's own creation. It's the format produced when you use their free Kindle Create software. While KPF files work perfectly on Kindle, they are designed exclusively for Amazon's ecosystem and won't work on other e-readers.

For authors seeking maximum control and compatibility, creating a validated EPUB file is the most professional route. It ensures your book is portable and can be adapted for any future platform, not just Amazon's.

How your book appears on screen is determined by its layout. There are two fundamental types: reflowable and fixed. A reflowable e-book acts like a fluid webpage. The text 'reflows' to fit the size of the screen and the reader's chosen font settings. This is the standard for most novels and text-heavy books because it provides the best and most customizable reading experience. A fixed-layout e-book is more like a PDF or a printed page. The elements—text, images, and graphics—are locked in place. This format is necessary for content where the visual arrangement is critical, such as children's picture books, comic books, or complex textbooks with multi-column layouts. While it gives the author complete control over the look, it can be difficult to read on smaller screens, as the user must pan and zoom to navigate the page.

For most authors, reflowable is the correct choice. It puts the reader's experience first and is what customers expect from a standard e-book.

A professional e-book isn't just a wall of text; it's a navigable file. Readers need to be able to jump to the beginning of any chapter easily. This is accomplished with two different, but equally important, tables of contents. First is the HTML Table of Contents. This is a page within your book, usually right after the title and copyright pages, that lists the chapters with hyperlinks. A reader can tap a chapter title to go directly to it. Second, and more critical for the e-reader itself, is the NCX file. This is a hidden, machine-readable file that powers the device's built-in navigation menu, often labeled "Go To" or "Contents." It allows readers to pull up the chapter list from anywhere in the book without having to flip back to the front. A quality e-book must have both.

You wouldn't publish a book without proofreading it, and the same principle applies to your e-book file. You must check for formatting errors that could create a frustrating experience for readers. The most important tool for this is Amazon's own Kindle Previewer. This free desktop software simulates how your e-book file will look on various Kindle devices, from e-ink readers to tablets and phones. It's essential for catching issues like images that are too small, text that overlaps, or broken links. The Previewer is your final line of defense before uploading.

Styling within your e-book is controlled by Cascading Style Sheets (CSS), the same language used to style websites. However, Kindle devices only support a limited subset of CSS properties. It's best to keep styling simple: focus on clear headings, paragraph indentation, and basic text formatting. Advanced layouts can easily break on older devices. Before you even get to the previewing stage, you should ensure your file is technically sound. An EPUB file is essentially a zipped collection of HTML and CSS files. For it to work correctly, it must be validated. Using a tool like the free, open-source EPUBCheck ensures your file's structure is correct and will be accepted by KDP and other retailers without issue.

Finally, don't forget about metadata embedding. Metadata is the data about your data: the book's title, author name, publisher, and ISBN. This information should be embedded directly within the EPUB file itself, not just entered on the KDP website. Embedding it ensures that no matter where your file goes, this crucial information travels with it, allowing reading systems and libraries to catalog it correctly.

Following these technical standards ensures your e-book looks professional and provides a seamless experience for your readers, which is crucial for earning good reviews and building a loyal audience.