You've probably heard for years that Kindles are a "walled garden." That they only play nice with Amazon’s own weird formats and if you have an EPUB or a PDF, you’re basically out of luck unless you spend an afternoon wrestling with conversion software.
Well, it's 2026, and the walls have mostly crumbled.
If you’re wondering what files does kindle use, the answer is actually a lot more flexible than it used to be. But there’s a catch. What the device "uses" and what it "accepts" are two different things. Amazon has finally leaned into the formats the rest of the world uses, though they still do some magic behind the scenes to make them look good on that E Ink screen.
The Big Shift: EPUB is Finally King (Sorta)
For a long time, EPUB was the one format Amazon refused to touch. Now? It’s basically the gold standard for getting your own documents onto a Kindle.
When you use the "Send to Kindle" service, Amazon takes that EPUB file and converts it into their own proprietary format, AZW3 (also known as Kindle Format 8) or KFX. They do this so you can still change the font, adjust the margins, and use all those "Enhanced Typesetting" features like better kerning and ligatures.
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But here is the massive news for 2026: As of January 20, Amazon actually started letting you download your purchased, DRM-free books back out as EPUB files. This is a huge deal. It means if you bought a book on Amazon that doesn't have digital rights management, you can finally move it to a Kobo or a Nook without feeling like a hacker.
What Files Can You Actually Sideload?
If you're plugging your Kindle into a laptop via USB—what we call "sideloading"—the list of what works natively is a bit shorter. Your Kindle won't just "see" an EPUB file if you drag and drop it into the documents folder. It’ll just sit there, invisible and useless.
For direct USB transfers, you generally need:
- AZW3 (.azw3): The modern standard for most Kindle books.
- KFX (.kfx): The "fancy" format that allows for the best-looking text.
- MOBI (.mobi): The old dinosaur. It still works, but it's buggy and doesn't support custom fonts well. Amazon has officially retired this for new uploads, but the hardware still reads it.
- PDF (.pdf): Great for things that need to look exactly like the print version, but a nightmare to read on a small 6-inch screen because you can't resize the text easily.
The Word Document Situation
Something kind of annoying happened recently. On February 9, 2026, Microsoft and Amazon officially pulled the plug on the "Send to Kindle" button inside Microsoft Word. You used to be able to just click a button in your doc and have it pop up on your Paperwhite.
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You can't do that anymore. Now, you have to go the old-fashioned route: save the .doc or .docx and upload it through the Amazon website or the mobile app. It’s an extra step, but honestly, the conversion quality is usually better when you do it that way.
Why the Kindle Scribe Changes the Rules
If you’re rocking a Kindle Scribe, the file conversation gets way more interesting. The Scribe thrives on PDFs.
Why? Because you can write on them.
When you send a PDF to a Scribe through the "Send to Kindle" service, it processes the file so you can use the stylus to jot down notes directly on the page. If you just drag-and-drop a PDF via USB, you lose that "on-page" writing ability—you'll only be able to use "sticky notes." It's a weird distinction, but one that matters if you're trying to grade papers or sign contracts.
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Comic Books and Manga: The KPF Factor
If you're a manga fan, you've probably run into KPF or MOBI/PRC for graphics. Amazon has a specific tool called Kindle Comic Creator that takes images (JPG, PNG) and turns them into a Kindle-friendly package.
These files are essentially containers for high-res images. They allow for "Guided View," which is that cool feature where the Kindle zooms in on individual panels so you aren't squinting at a tiny speech bubble.
A Quick Cheat Sheet for 2026
I know this gets technical, so let's simplify it.
If you have a file and want it on your Kindle, here is the move:
- Got an EPUB? Use the "Send to Kindle" web tool or app. Don't use USB.
- Got a PDF? Use USB if you just want to read it; use "Send to Kindle" if you want to write on it (Scribe only).
- Got a Word Doc? Use the "Send to Kindle" website. The built-in Word feature is dead.
- Got a bunch of random files? Download Calibre. It’s free software that has been the "secret weapon" for Kindle power users for a decade. It’ll turn anything into a KFX or AZW3 file in seconds.
Final Actionable Steps
Stop worrying about finding the "perfect" file format before you buy or download a book.
Basically, as long as it's an EPUB, you're good. Just head over to the Amazon Send to Kindle page, drag your file there, and let their servers do the heavy lifting. Within two minutes, it'll show up in your library, fully formatted and ready to read. If you’re dealing with DRM-free books you already own on Amazon, go to your "Manage Your Content and Devices" page and see if the new EPUB download option is active for your library yet—it’s rolling out to more titles every week this year.