the format situation is both simple and a bit nuanced. Kindle primarily supports its proprietary AZW and AZW3 formats, which are essentially enhanced versions of MOBI. These work seamlessly across all Kindle devices and apps. EPUB, the most common ebook format, isn't natively supported, but Amazon's got a workaround—you can email EPUBs to your Kindle address, and their servers convert them automatically. It's like magic, though sometimes the formatting gets a little wonky with complex layouts.
KFX is Amazon's newest format, packing cool features like enhanced typography and page numbers, but it's only for newer devices. If you're sideloading books via USB, MOBI still works on older Kindles, but it's being phased out. PDFs are technically supported, but reading them on a Kindle is like trying to fit a square peg in a round hole—doable, but not pleasant. Personally, I stick to AZW3 for purchased books and converted EPUBs for everything else. The key is knowing your device's generation and using tools like Calibre to manage formats.