Here is an example. I have a Kindle version of the Modern Hebrew NT from Logos when they had send to Kindle, and my own pdf version of it. If I pinch and zoom or change font size in the Kindle version, it resets the margins automatically as you would expect. But if I pinch and zoom on my pdf to make it larger, yes, I lose part of the page off the screen. And, navigating to the other parts off the screen is not as smooth, responsive, or as fast as on an iPad or Android tablet. It's much preferable to have a pdf with a full page on the screen, and just tap to the next page.
Even if I'm in landscape mode reading my HNT pdf, it cuts the page in half, and sometimes tapping or swiping between top and bottom halves does not work smoothly, i.e., you have to take a second to find out where you were. It will be much more enjoyable for me to just remake these types of pdfs.