

Fine for personal use, but useless for publishing. Obviously, that format, then, lacks utility.

You can certainly make a file in that format, and side-load it to your own Kindle device, but you can't publish it. However, just like AZW, you can't upload an AZW3 file format at the KDP.
#Kindle file format compatibility software
The latter, AZW3, is a file format, created to emulate what's called "KF8," (the more-advanced Kindle formatting) by a piece of free library software called Calibre. And, even if you could, you can't upload that format at the KDP, the Kindle Digital Publishing platform. That's not a format that you can make yourself. The former (was/is) the actual, final, encrypted Kindle format that is dispensed from the Amazon store, to your Kindle as a purchased book. Now, if you've run across various forums, you may have seen people refer to AZW format, or AZW3 format. If you try to upload a MOBI file for a reflowable ebook, you’ll be stopped dead in your tracks. MOBI is still accepted, by Amazon, in certain special cases-those being for what are called Print Replica files (for example, heavy photography books or illustrated children’s books) where the placement of text and images is absolutely crucial and cannot be altered or “reflowed” as text does in regular eBooks when you change font size or screen size or rotate the device. But the process that used to intake a MOBI file, perform nominal conversions or changes to it and spit out a file that was optimized for the myriad Kindle devices, no longer exists, at least, not for typical, everyday reflowable eBook files (your typical novel, memoir, self-help book, etc.) Today, if you want to upload a reflowable eBook, you need ePUB format, not MOBI. This does not mean that you can’t upload a Word file, still you can. The bottom line is, as of midsummer 2021, the files that Amazon sells to its readers are, by and large, derived from the last-man-standing eBook format, which is ePUB. If you've Googled, you've likely seen all sorts of claims, ranging from some folks telling you that you can put an ePUB (directly) on a Kindle device, to the idea that using Word is the best "Kindle eBook format."
