technically, I think that was was encountered here was a
fixed format e book
https://www.millcitypress.net/author...d-layout-ebook
the file extension is not a reliable guide to what's inside, in these cases. Peeking at the code is the only way I know of to be sure
I have encountered it once before in a game guide that I bought from amazon ( it downloaded as azw) and I gave up trying to convert it once I looked inside). My book would zoom in and out ok, in a kindle for android app, but it would not reflow. Sometimes, amazon may say "print replica" somewhere in the small print on the web site listings for such books