Kindle Supported Formats and How to Convert for Your Device
What Kindle Actually Supports (The Full List)
Amazon has quietly expanded Kindle's native format support over the years, but plenty of confusion remains about what works out of the box versus what requires conversion. As of 2025, Kindle devices and the Kindle app natively support the following formats: AZW3 (Amazon's primary e-book format), MOBI (older Amazon format, still readable on most devices), KFX (the newer Kindle Format 10, used for enhanced typography), PDF, TXT, HTML, DOC and DOCX, RTF, JPEG, GIF, PNG, BMP, and EPUB — though EPUB support was only added in 2022 and applies to Kindle firmware 5.16.2.1.1 and later. The most important thing to understand is that 'supported' doesn't always mean 'well-supported.' PDFs, for example, open on every Kindle, but the reading experience on a 6-inch Paperwhite can be genuinely terrible for a document formatted for A4 paper. Text reflow is hit-or-miss, footnotes often break, and complex tables become unreadable. TXT files work fine for plain text but strip out all formatting. DOCX files render acceptably for simple documents but struggle with anything using custom fonts, tracked changes, or complex styles. EPUB is the global standard for e-books and is used by virtually every other platform — Kobo, Apple Books, Google Play Books, and public library systems like OverDrive all use EPUB as their primary format. Kindle's late adoption means that older Kindles (anything running firmware below 5.16.2) still cannot open EPUB files at all. If you own a Kindle Keyboard, a Kindle 4, or an older Paperwhite and haven't updated firmware, EPUB remains unsupported on your device. Always check your firmware version under Settings > Device Options > Device Info before assuming you can sideload an EPUB.
The Formats Kindle Cannot Handle
Knowing the gaps matters as much as knowing the supported list. Kindle has no native support for CBZ or CBR files (the standard formats for digital comics), DJVU (common for scanned academic texts and older technical manuals), FB2 (popular in Eastern Europe and Russia), LIT (Microsoft's defunct e-book format), ODF, or any audio/video formats beyond the basic multimedia embedded in KFX files on newer devices. CBZ is worth dwelling on because it's a real pain point for comic readers. A CBZ file is essentially a ZIP archive containing sequentially named image files. Kindle's Comixology integration handles comics purchased through Amazon, but if you have a personal collection of CBZ files — scanned manga, indie comics, or anything from Humble Bundle — you cannot simply transfer them to a Kindle and expect them to open. You need to convert them first, typically to a PDF or, better, to a format like MOBI or AZW3 with the images properly embedded and sized for your device's specific resolution. DJVU is another common stumbling block for researchers and academics. Many digitized books from university libraries and Internet Archive are distributed as DJVU files because the format compresses scanned pages extremely efficiently. A 400-page scanned book might be 8 MB as DJVU versus 80 MB as PDF. Kindle simply cannot read DJVU, so conversion is mandatory. The quality of that conversion — particularly how well the OCR text layer is preserved — varies significantly depending on the tool you use. LIT files are rare now but still circulate among people who bought e-books in the early 2000s through Microsoft Reader. If you have an old LIT library, conversion is your only option, and you should do it sooner rather than later since fewer tools support LIT with each passing year.
Converting EPUB to Kindle Format: What You Need to Know
Despite Kindle's newer EPUB support, there are still good reasons to convert EPUB files to AZW3 or MOBI before sending them to your device. Converted files tend to have better typography rendering on older firmware, and the Send to Kindle service — which lets you email documents directly to your Kindle's assigned address — handles MOBI and AZW3 more reliably than EPUB in practice. Using CocoConvert, the process is straightforward: upload your EPUB file, select AZW3 or MOBI as the output format, and download the converted file. For most fiction e-books — a novel with chapters, a standard table of contents, and no complex formatting — this produces a clean result. The chapter navigation works, the font settings on your Kindle respond correctly, and the file size is reasonable. Where things get more complicated is with EPUBs that use fixed layouts. Fixed-layout EPUBs are common for children's picture books, cookbooks with precise image placement, and technical books where diagrams sit alongside specific paragraphs. These files are designed so that the text and images cannot reflow — the layout is fixed at specific pixel positions. Converting a fixed-layout EPUB to MOBI or AZW3 often produces a mess: images that overlap text, chapters that lose their visual structure, or pages that render as blank. CocoConvert will complete the conversion, but we want to be honest: the output quality for fixed-layout EPUBs is unpredictable, and you may get better results converting to PDF instead and accepting the reflow limitations. For reflowable EPUBs — which covers the vast majority of novels, memoirs, essays, and standard non-fiction — conversion quality is consistently good. The one setting worth checking after conversion is the table of contents. If your EPUB uses an NCX file for navigation (older EPUB 2 standard) rather than an EPUB 3 nav document, the converted Kindle file should preserve chapter navigation correctly. If the TOC is missing after conversion, it usually means the source EPUB had a malformed or absent navigation file to begin with.
Converting PDF to Kindle: Managing Expectations
PDF-to-Kindle conversion is the most requested and most misunderstood conversion task. People assume that because Kindle supports PDF natively, converting a PDF to MOBI or AZW3 will produce a clean, reflowable e-book. Sometimes it does. More often, the result requires careful review. The core problem is that PDF is a presentation format, not a semantic document format. A PDF doesn't know that a block of text is a chapter heading versus body text — it just knows that certain characters appear at certain coordinates on a page in a certain font size. When a conversion tool processes a PDF, it has to infer document structure from visual cues: larger text is probably a heading, indented text is probably a quote, two-column layout probably means the columns should be read separately. This inference works well for clean, well-structured PDFs like academic papers or professionally typeset books. It works poorly for scanned PDFs without an OCR layer, PDFs with unusual layouts, or PDFs that use images instead of actual text. For a practical example: take a standard 300-page business book saved as a PDF by the publisher. Converting it through CocoConvert to AZW3 will typically produce a readable Kindle file with correct chapter breaks and working navigation. The conversion takes the embedded text, reflows it for the Kindle's screen, and rebuilds the document structure. Font sizes from the original PDF are used to guess heading levels. Now take a scanned 1960s technical manual saved as a PDF with no OCR layer — just images of pages. Converting that to AZW3 produces a file that is essentially a sequence of images. It will open on your Kindle, but you cannot adjust font size, search the text, or use the built-in dictionary. For scanned PDFs, you need OCR processing before or during conversion, which is a separate step. CocoConvert does not currently perform OCR as part of the PDF-to-Kindle conversion pipeline, so if your source PDF is image-only, the output will be image-only. A practical workaround for dense academic PDFs: convert to MOBI, then sideload using the Kindle's USB connection rather than Send to Kindle. Files above 50 MB can hit size limits with email delivery, and USB transfer bypasses that entirely.
Privacy Considerations When Converting Personal Documents
This section matters more than most people realize. When you convert a file using any online service — including CocoConvert — you are uploading that file to a server. For a novel you downloaded from Project Gutenberg, this is a non-issue. For a PDF of your employment contract, your medical records, a confidential business report, or your personal journal, it deserves serious thought. CocoConvert processes uploaded files for conversion and does not store them beyond the conversion session. Files are automatically deleted from our servers within one hour of upload, and we do not use file contents for any purpose beyond performing the requested conversion. We do not train machine learning models on uploaded content, and we do not share files with third parties. That said, no online service should be your first choice for genuinely sensitive documents. If you need to convert a document containing personal financial data, medical information, legal documents, or anything covered by your employer's confidentiality policies, the right tool is a local application installed on your own machine. Calibre — the open-source e-book management application — performs the same EPUB-to-MOBI and PDF-to-MOBI conversions entirely on your computer, with no data leaving your device. It's free, runs on Windows, macOS, and Linux, and handles the vast majority of conversion tasks that CocoConvert handles. For documents that are not sensitive — public domain books, freely available articles, personal creative writing you're comfortable uploading — online conversion is faster and more convenient than installing and configuring a local application. The honest framing is this: use CocoConvert for convenience when privacy isn't a concern, and use Calibre when it is. Both tools have their place, and anyone who tells you an online conversion service is always the right choice for every document type is not giving you complete information.
Sideloading Converted Files to Your Kindle
Once you have a converted file, getting it onto your Kindle is straightforward, but the method matters depending on your device and file type. The easiest method for most people is Send to Kindle. Every Kindle account has an associated email address, which you can find at Amazon.com under Account & Lists > Content & Devices > Devices > [your device] > Send-to-Kindle Email. You email the converted file as an attachment to that address from an email address you've approved in your Amazon account settings (under Personal Document Settings > Approved Personal Document E-mail List). The file appears in your Kindle library within a few minutes. This works well for MOBI, AZW3, PDF, DOCX, and TXT files. The 50 MB attachment limit applies, which rules out large PDFs and some image-heavy conversions. For larger files or for users who prefer not to route documents through Amazon's servers, USB transfer is the alternative. Connect your Kindle to your computer with a USB cable. It mounts as a standard storage device. Open the drive and navigate to the 'documents' folder. Drag your converted file into that folder. Eject the Kindle and disconnect. The file appears in your library immediately. This method works for any format Kindle supports and has no file size limit beyond your device's available storage. One important note about USB transfer and EPUB files: even on newer Kindles with EPUB support, EPUB files transferred via USB may not appear in your library on some firmware versions. If an EPUB you transferred via USB isn't showing up, try renaming the file extension to .epub (lowercase) and retransferring, or convert it to AZW3 first. This is an Amazon firmware quirk that has been reported across multiple Paperwhite and Kindle Basic models. The Kindle app on iOS and Android accepts files differently. On iOS, use the Share sheet and select 'Copy to Kindle.' On Android, open the file with any file manager and choose 'Open with Kindle' from the share menu. Both methods work with MOBI, AZW3, PDF, and EPUB files.
Choosing the Right Output Format for Your Specific Use Case
Not every conversion destination is equal, and the right output format depends on what you're converting and how you plan to read it. For standard e-books — novels, essays, non-fiction without heavy visual formatting — AZW3 is the best output format for Kindle. It supports the widest range of Kindle typography features, handles large files efficiently, and is the format Amazon itself uses for books sold through the Kindle Store. If you're on older firmware that predates AZW3 support (Kindle 2, Kindle DX, very old Paperwhite models), use MOBI instead. For documents you primarily want to read without reformatting — a research paper, a newsletter, a magazine article saved from the web — PDF is often the better choice despite its reflow limitations. A well-formatted PDF viewed on a Kindle Scribe (10.2-inch screen) or a Kindle Paperwhite with the zoom function is perfectly readable. The same PDF on a basic 6-inch Kindle in portrait mode will require constant zooming and panning. Know your device's screen size before deciding. For comics and manga, the ideal format is CBZ converted to a Kindle-optimized PDF or to a Panel View-compatible format. The Kindle's Panel View feature — available on Kindle Fire tablets and the Kindle app, though not on e-ink devices — automatically detects comic panels and lets you tap through them individually. For e-ink Kindles, a PDF with pages sized to your device's exact resolution (1072x1448 pixels for Paperwhite 11th generation, for example) gives the sharpest image quality. For academic and research documents where searchability matters, always ensure your source PDF has an actual text layer before converting. If it doesn't, run it through an OCR tool first. A searchable AZW3 file where you can highlight passages and look up terms in the built-in dictionary is dramatically more useful than an image-based PDF where none of those features work. The extra step of OCR processing before conversion is worth the time.