Difficulty sharing Adobe Reader pdf files using Share function of Zoom on a MacBook

Hi all. I’m new to MacBooks and have been having a heck of a time figuring out how to successfully share a pdf file a set of pdf’s.  I’m using the latest version of Zoom and the latest Mac ios.  What is happening is when I go to Share, I can see the pdf files as in little pdf preview square with the file name below.  Some of the boxes have no preview in them and only have file names beneath.  When I try to load those files, nothing is displayed on the share screen.  I have tried everything I can find on Google including making sure Adobe pdf documents are separated and not as a bunch of tabs in one window, and setting “prefer tabs when opening documents” to Never in Mac settings.  I have had to resort to simply sharing the entire desktop and then selecting whatever specific pdf I want to share that way, but this is cumbersome and primitive.  It doesn’t look professional in my opinion to have a Zoom call and have a client view your entire desktop screen until you bring up the proper document you want to share.

So if someone can point me in the right direction as to how to solve this, I would greatly appreciate it.   
Thanks in advance for ANY help.