Your latest suggestion triggered an idea. I'd actually wanted to replace Adobe so did not reinstall after the last time. But your comment made me think that perhaps there is something actually in a pdf reader that the viewer needs. So, I deleted everything again and ran the windows file checker utility, cleared Explorer's history to "clean and reset" my system. I then reinstalled Adobe Reader. After making sure Explorer still worked, then I installed DOpus. It worked! My viewer is operational again.
Thanks for hanging in there with me to try to figure things out. I will make note of all your other suggestions just in case the current fix doesn't stick. Enjoy the rest of your weekend!