What is an ebook?
The text is reflowable (unless it isn’t) While PDFs are literally impossible to edit, they still don’t qualify as ebooks: if you have ever tried reading a PDF on a tiny screen, you perfectly know why. You can’t change the layout: reading a PDF on an e-reader device is almost as uncomfortable as photographing a whole book and reading that (which is something none of us would ever do, obviously). PDF is the ideal format for printed books: it is designed with the exact paper size in mind. It always looks like the print version. Never changes.
Ebooks, on the other hand, are created in a format that changes shape according to the device you read it on. You will still have chapters and paragraphs, but the line breaks aren’t forced: it will always perfectly fill your screen. You expect websites to change their layouts when you are looking at them from your tablet or phone; the same goes for epubs. The epub 3 standards, however, introduced fixed-layout epubs: everything on the screen has an absolute position. Fixed-layout epubs lose much of their adaptability but still recognise the device and app they are displayed with.
With that in mind, and you still want to put your book on a Kindle, you might want to look at the KDP Guidelines. https://kdp.amazon.com/en_US/help/topic/GU72M65VRFPH43L6 And if you are searching for another format, you can look here. https://kdp.amazon.com/en_US/help/topic/G200634390
Both make very interesting reading. To confuse matters even more, generally, the Kindle App found on Macs and PCs will happily display ebooks done in PDF format. But the handheld readers won’t. …
and lastly, if you are determined to produce your book for the e-reader market, here’s the latest comparison list from Wikipedia. https://en.wikipedia.org/wiki/Comparison_of_e-readers