KDP accepts several manuscript formats for ebooks, including Microsoft Word (DOC/DOCX), EPUB, and Kindle Package Format (KPF), along with HTML, RTF, plain text and — for a limited set of languages — PDF. MOBI is gone: support ended for reflowable books in 2021 and for fixed-layout books in March 2025.
So both of the formats most authors have are accepted, and the upload will succeed either way. The real question is not what Amazon will take. It is which one leaves the decisions with you.
Short answer: upload an EPUB if you care what the chapter navigation looks like. Upload Word if you would rather Amazon decided that for you.
What happens to a Word file
Amazon converts it. A .docx is not an ebook — it is a word processing document — so KDP runs its own conversion to produce the reflowable file readers actually get.
That conversion is competent and completely out of your hands. It reads your document's structure and makes its own decisions about what is a chapter, where one ends, and what belongs in the navigation menu.
Which is fine when your document is cleanly structured, and much less fine when it is not. The usual failure is the one that catches everyone:
A chapter title styled by selecting the line and making it 18pt, bold and centred is, structurally, a paragraph that happens to look large. A chapter title styled as Heading 1 is a heading.
They are indistinguishable on your screen. Only one of them becomes an entry in the reader's Go To menu. If you have ever uploaded a novel and found the chapter list empty, that is what happened — and the file was never rejected, because nothing about it was invalid.
What happens to an EPUB
Nothing much, which is the point.
An EPUB is already the thing a Kindle reads. Amazon converts it to its own internal format for delivery, but the structure — the chapter list, the reading order, the metadata — is already decided inside the file you uploaded, and that decision travels with it.
Concretely, you control:
- The navigation document. The chapter menu is a literal list of links in
nav.xhtml. You can open it and read it before you upload anything. - The metadata.
dc:titleanddc:creatorare in the package document. This is what a store lists the book under, and it is the reason ebooks occasionally appear for sale as "Untitled". - The reading order, including where front matter sits.
And you can check all of it. Run EPUBCheck on the file and you get a report on whether it is structurally sound, before Amazon ever sees it. There is no equivalent for a .docx — the first indication that a Word conversion went wrong is usually a reader mentioning it.
The case for each
Upload Word when the book is a straightforward run of chapters with no front matter to speak of, your headings are genuinely styled as headings, and you have no strong feelings about the navigation. Amazon's converter will do a reasonable job and you will have saved yourself a step.
Upload EPUB when the book has real front matter, when the chapter list matters to you, when you are also publishing to Apple Books or Kobo — they take EPUB and not .docx, so you need one anyway — or when you have already uploaded a Word file once and something came out wrong.
That last case is the common one. Most people arrive at EPUB after a Word upload produced a book with no chapter navigation, and the fix is not to fight the converter but to stop using it.
A note on Kindle Create and KPF
Kindle Create is Amazon's own tool. It produces KPF, which is Amazon's format and works only on Amazon.
It is a perfectly good route if Amazon is the only place you are publishing. It is a dead end if it is not: a KPF file cannot be uploaded to Apple Books, Kobo or Google Play Books, so you would be building the book twice.
If there is any chance you will publish wide, build the EPUB. It works on Amazon and everywhere else, and Kindle Create can import one if you later want its layout features.
What this site does
The Kindle formatter returns both from the same manuscript: a reflowable EPUB with real chapter navigation, and a structured DOCX with the headings marked up properly.
Both, deliberately. The EPUB is the one to upload if you want the navigation you can see; the DOCX is there because some people prefer to hand Amazon a Word file and let it convert, and because Kindle Create will open it. What matters is that the DOCX has its headings marked as headings, so if you do let Amazon convert it, the conversion has something real to read.