Kindle Ebook File Types: EPUB, MOBI, KFX, KPF, and What KDP Accepts Now
Understand current Kindle file types: which formats authors can upload to KDP, why MOBI is legacy, what KFX means, and when to use EPUB, KPF, or DOCX.
Authors preparing a KDP ebook often encounter a confusing alphabet soup of file format names: EPUB, MOBI, KFX, AZW, AZW3, KPF: and aren’t sure which they need, which KDP accepts, and which will produce the best result for readers. The short answer is: submit EPUB and let KDP handle the conversion. The longer answer involves understanding what each format actually is, because it affects your formatting workflow, your choice of tools, and your understanding of what readers actually receive on their devices.
The Kindle Format Ecosystem in Plain English
Several acronyms appear in Kindle discussions because the ecosystem contains source files, author-upload formats, Amazon conversion formats, and device-delivery formats. They are not interchangeable. The practical question for an author is simpler: what file should I create and upload today?
For most ordinary reflowable books, build a clean EPUB, KPF, or DOCX workflow. KDP converts that source into the formats needed for supported Kindle apps and devices.
Keeping these layers separate also makes troubleshooting easier. If an EPUB validates but the Kindle preview is wrong, you have a conversion/rendering problem to investigate. If the EPUB itself fails validation, fix the publishing source before blaming the Kindle device format.
EPUB: The Best General-Purpose Choice
EPUB is an open publishing standard and the strongest general choice when you want a portable ebook source that can also be used outside Amazon. A well-formed EPUB supports semantic headings, navigation, images, links, accessibility information, and responsive reflow.
Use EPUBCheck during production and Kindle Previewer before KDP submission. Passing EPUB validation does not guarantee beautiful Kindle rendering, but it catches structural errors before Amazon’s conversion step.
EPUB 3 is the current standards-based ecosystem for modern ebooks and supports accessibility metadata and richer semantic structure. For a simple novel you may use only a fraction of those capabilities, but maintaining a standards-based master gives you a cleaner route to other retailers and future updates.
KPF: Kindle Create’s KDP-Focused Output
KPF is the Kindle Package Format produced by Kindle Create. It is useful for authors who want Amazon’s free authoring tool to handle the Kindle-focused project and export. It is not an open distribution format in the same way as EPUB, so authors publishing widely may prefer to maintain an EPUB master as well.
KPF can be convenient for straightforward text books and supported richer layouts, but keep the editable project files and original manuscript. The exported package should never be the only copy of your production source.
Kindle Create can also simplify recurring book structures such as chapter titles and theme styling. The trade-off is ecosystem dependence: if you later move to another retailer, you still need a portable source such as DOCX or EPUB rather than treating KPF as your universal archive.
DOCX: Useful for Straightforward Reflowable Books
KDP can accept DOCX for many normal reflowable books. A clean Word document with real styles, simple images, correct page breaks, and no manual layout tricks can convert successfully. Complex layouts, tables, sidebars, and heavily styled nonfiction usually benefit from a dedicated ebook production workflow.
If Word is your source, remove print-only headers, footers, page numbers, tabs used for alignment, and repeated blank lines before upload. Preview the converted result rather than assuming the Word page view represents Kindle.
Use Word styles for headings and body text and keep the document semantically simple. A DOCX full of floating text boxes, manually positioned images, section-specific font hacks, and print page geometry is a poor candidate for automatic reflow.
MOBI: Legacy, Not a Current KDP Upload Format
MOBI dominated older Kindle tutorials, which is why it still appears in search results. KDP has now completed the transition away from MOBI uploads. Authors should not build a new production workflow around exporting or validating MOBI for submission.
Old MOBI files can still exist in personal libraries and historical workflows, but that does not make MOBI a current KDP author-upload choice. Replace outdated tutorial steps with EPUB, KPF, or DOCX.
This is also a useful quality check when hiring a formatter. If a 2026 delivery package is built around “MOBI for Amazon” with no explanation that KDP no longer accepts MOBI uploads, ask the supplier what current source and validation workflow they actually use.
KFX, AZW, and AZW3: Delivery-Ecosystem Formats
KFX is associated with modern Kindle delivery and rendering; AZW and AZW3 are older Amazon-specific Kindle formats. These are useful terms for understanding what may exist on devices or in historical technical discussions, but most KDP authors do not need to manufacture them for upload.
If your goal is to publish a book, optimize the source EPUB/KPF/DOCX and test the customer-facing result. Trying to reverse-engineer Amazon’s delivery package adds complexity without improving the author submission workflow.
Readers may still encounter these extensions when sideloading, backing up old devices, or discussing Kindle software. That technical history is real, but it should not dictate the production specification you give a formatter for a new KDP release.
Fixed Layout and Image-Heavy Books Need a Different Decision
Children’s picture books, comics, cookbooks, and other layout-dependent works may need fixed-layout production rather than a normal reflowable EPUB. KDP’s supported fixed-layout workflows differ by book type, and accessibility/readability trade-offs are larger because the page cannot simply reflow around the reader’s chosen font size.
Choose fixed layout because the content requires spatial relationships, not because it seems easier to preserve a print design. A print PDF converted into image-like pages is usually a poor substitute for a properly built ebook.
Fixed layout can preserve a designed page, but it reduces the flexibility readers have to resize and reflow text. Test it on the actual device classes you expect your audience to use, and consider whether the same content also needs a print edition or accessible alternative.
File Size Still Matters
Large images and inefficient assets increase file size and can affect delivery economics in royalty scenarios where delivery cost applies. Compress images intelligently without making them visibly poor. Remove duplicate assets, oversized images, embedded junk, and unused fonts or media from the source package. Use the Kindle ebook pricing guide to model current royalty and delivery-cost implications rather than relying on an old per-megabyte example copied from a blog post.
Measure image dimensions at their displayed use rather than exporting every asset at a huge camera resolution. Efficient assets can keep a book responsive and reduce unnecessary delivery weight without sacrificing visible quality.
The Practical Upload Workflow
Create the source in your chosen tool, validate it, preview it, upload to KDP, and inspect the converted preview again. After publication, check the retail sample and live device/app experience when available. Keep the editable source so later corrections can be generated consistently.
File-format decisions should disappear into the production system once made. The reader should experience a clean book, not evidence that the author spent days debating acronyms.
Keep a release checklist with the source filename, validation result, Previewer version/date, KDP upload date, and any conversion warnings. That small record becomes valuable when you update the book months later and need to know which file actually produced the live edition.
Frequently Asked Questions
Does KDP accept MOBI in 2026?
No. MOBI is a legacy Kindle format and is no longer accepted as a KDP ebook upload format.
Should I upload KFX to KDP?
No. KFX is associated with Amazon’s Kindle delivery ecosystem, not the normal author upload format.
Is EPUB better than DOCX?
EPUB gives more explicit control and portability. A clean DOCX can work well for straightforward reflowable books, especially when the styles are simple.
What is a KPF file?
KPF is the Kindle Package Format exported by Kindle Create for KDP-focused production.
Can I use the same EPUB on other retailers?
A standards-compliant EPUB is designed to be portable, although each retailer can have its own validation and content requirements. Test on every platform you distribute through.
What to Do Next
Choose one master workflow: EPUB for maximum portability, KPF if Kindle Create is your production tool, or clean DOCX for a simple book. Validate and preview that source, and stop maintaining legacy MOBI files for new KDP uploads.
Finish the text before you lock the production files. Vappingo’s qualified native-English editors can proofread the manuscript and publication-facing copy so formatting and upload are built on a clean source.
