When you say reading the Kindle format books on Dropbox what do you mean exactly, Margia? Are you trying to read them in Dropbox? Probably not, I guess.
I can tell you what I’m doing on my phone - though it’ll be no help if you have a different set up.
From the Kindle format file I open a book and tap the three dots in the top right hand corner of the screen. This brings up a menu. Scroll down to Export. Tap that - and from the choices available select Copy to Kindle. Then it’s exported to the Kindle app on my phone. It works beautifully.
(Before we had the Kindle ready ebooks only a few would export to my Kindle app. Most of the rest I could export to iBooks. A few had to be read directly from Dropbox.)
Hope someone else can help if my method is useless to you.