What file do I upload to Amazon KDP now?

An EPUB. KDP retired the MOBI format for reflowable ebooks and converts the EPUB you upload into its own formats on its side. Kindle Create's KPF files are also accepted, but the EPUB is the standard route, and the same file you validate locally is the one the converter receives.

As a publishing format, yes. It is a twenty-year-old format that stopped gaining features years ago, Amazon stopped accepting it for new reflowable uploads, and Send to Kindle now takes EPUB. Old MOBI files already published keep working; nothing new should be built in it.

What is the difference between a reflowable and a fixed-layout EPUB?

A reflowable EPUB has no pages: text flows to fit the reader's screen and chosen type size, which is what novels and most nonfiction want. A fixed-layout EPUB pins each page's design in place — picture books, comics, cookbooks where the composition is the content — at the cost of the reader's controls. They are different products built from different sources.

Why not just upload a PDF?

Because a PDF is a printed page photographed. On a phone it is a postage stamp; text does not reflow, cannot be resized usefully, and the retailer's reading systems treat it as a scan. PDFs are the format of print — a print-ready PDF goes to a press, never to an e-reader.

EPUB, MOBI, and the formats bookstores actually want

The file-format question in publishing is smaller than it looks, because the industry has consolidated around one answer: make an EPUB. Everything else is either an internal conversion someone else performs, a print format, or history. But the history still gets asked about, and the one real distinction — reflowable against fixed layout — is genuinely important.

EPUB: the format the industry agreed on

An EPUB is a ZIP package of HTML files, styles and images, with metadata and a navigation document — in effect, a small website describing a book, wrapped to a standard. That construction is the source of both its strengths and its quirks: the text is real text that reflows to any screen and any type size the reader chooses, and everything the book contains is inspectable and convertible.

It is the format every major retailer accepts directly — Apple Books, Kobo, Google Play, Barnes & Noble — and the one Amazon converts from. It is also what libraries lend through their apps. One file serves all of them, provided it is built well; the errors that get one rejected are covered in why your EPUB was rejected.

MOBI: the format that lost

MOBI was Kindle’s native format for most of two decades, and self-publishers built their mental model around it: “convert to MOBI for Amazon”. That model is out of date.

Amazon stopped accepting new MOBI uploads for reflowable ebooks, retired the conversion tools, and now takes the EPUB and converts it on their side. Send to Kindle accepts EPUB. The format itself froze years before that — it never gained the features modern EPUBs carry, which is why it lost.

The practical residue: files already published as MOBI keep working, nothing new should be made in the format, and any guide still telling you to convert your EPUB to MOBI is describing a world that has ended. The word survives in a few retailer help pages and a lot of forum posts, which is why the question keeps being asked.

KPF is Kindle Create’s package format — a convenience route Amazon still accepts. It is not required, and choosing it binds the book to one tool; the EPUB is the portable choice.

PDF: the format of print, and only print

A print-ready PDF is a different object from an ebook: fixed pages, embedded fonts, exact dimensions — the requirements are the print-ready checklist. It goes to a press or a print-on-demand service.

As an ebook, a PDF is what you produce when the page design is the product and you accept the costs: no reflow, tiny text on phones, no reader settings honoured. Retailers accept PDFs for some categories, and readers regret them. The honest rule: if the book is meant to be read in the hands, it is an EPUB; if it is meant to be printed, it is a PDF. A few books — art, complex reference — genuinely are page-objects, and for them the fixed-layout EPUB exists.

The one real distinction: reflowable vs fixed layout

Everything above sorts into two kinds of book.

Reflowable — the default for anything read as text. No pages; the reader’s device and type choice decide the layout. This is where everything an ebook does not control applies, and it is what “EPUB” means in most conversations.

Fixed-layout EPUB — each page rendered as designed, like a PDF that reading systems can page through. For picture books, comics, and heavily designed cookbooks, it is the correct product: the composition is the content, and reflowing it would destroy it. The costs are real: readers cannot change the type size, so accessibility work moves to the page design itself, and the file is built page by page rather than flowing from the text.

The mistake to avoid is choosing fixed layout because the book looks designed that way in your editor. A novel with a pretty chapter opening is still a reflowable book; the opening is one styled page at the start of flowing text. Fixed layout is for books where every page is composition.

What you actually make

The working recipe for a typical book:

One EPUB, reflowable, well-built and validated — it uploads to every retailer and every library platform.
One print-ready PDF, at the chosen trim, with fonts embedded — it uploads to KDP, IngramSpark or any printer.
A cover in each wrapper the destinations need — an image for the ebook listing, a wrapped print file for the interior, per setting up a cover file.

Two files and a cover, made from one book. Every other extension in the ecosystem — MOBI, AZW, KFX — is something a platform derives from these, not something you produce.

The formats settled while nobody was announcing it: EPUB for reading, PDF for printing, everything else generated downstream. The craft has moved to making the EPUB genuinely good — structure, navigation, notes and images that survive every screen.

Nueel exports both from the same book: a print-ready PDF from the paginated design and a reflowable EPUB from the same text, so the two artefacts agree because they were never two projects.

Common questions

What file do I upload to Amazon KDP now?: An EPUB. KDP retired the MOBI format for reflowable ebooks and converts the EPUB you upload into its own formats on its side. Kindle Create's KPF files are also accepted, but the EPUB is the standard route, and the same file you validate locally is the one the converter receives.
Is MOBI dead?: As a publishing format, yes. It is a twenty-year-old format that stopped gaining features years ago, Amazon stopped accepting it for new reflowable uploads, and Send to Kindle now takes EPUB. Old MOBI files already published keep working; nothing new should be built in it.
What is the difference between a reflowable and a fixed-layout EPUB?: A reflowable EPUB has no pages: text flows to fit the reader's screen and chosen type size, which is what novels and most nonfiction want. A fixed-layout EPUB pins each page's design in place — picture books, comics, cookbooks where the composition is the content — at the cost of the reader's controls. They are different products built from different sources.
Why not just upload a PDF?: Because a PDF is a printed page photographed. On a phone it is a postage stamp; text does not reflow, cannot be resized usefully, and the retailer's reading systems treat it as a scan. PDFs are the format of print — a print-ready PDF goes to a press, never to an e-reader.