I believe I've found the problem. I have a HP computer and apparently HP decided that their HP Sure Click software needed to be running on my computer. After doing a lot of searching, I discovered that the HP Sure Click software could be disabled which I did. After restarting my computer, PDF files opened in any fashion function as I want them to: opening the files in ONE iteration of Adobe Reader DC. The version of Adobe reader DC that is running on my computer is 2021.005.20058. Hopefully