Solved: Adobe Acrobat DC and pdf files will not open

Longtime problem just happened to me:  Found myself unable to open long-time much-used pdf files.  I use Adobe Acrobat DC free version.  Many old threads here, not all the same setup.  I'm running Windows 10, fully updated and secure.  First sign of a problem appeared a few days before I lost access.  I noticed that when I opened up my old pdf (a foreign-language textbook for English-speakers) I was being asked for permission to open the file.  Then I lost access.  Click on a shortcut or a file and then give permission . . . and, nothing.  Task Manager showed usual Adobe activity.  Came here.  Yes, of course, open Adobe.  Same thing!  The Adobe user interface would not open.  Scanned for malware.  Updated.  Ran Windows housekeeping.  Ran compatibility check, tried suggested "Windows 8" setting.  Tried repairing Adobe.  Uninstalled/reinstalled Adobe.  Nothing.  Kept coming back here.  No help, despite some users having solved their problem in the past.  Note, in my case I could still open pdf files on various websites (using Chrome as browser).

OK, what can System Restore do for me?  A single restore point was offered by Windows, going back 4 days.  Showed that major monthly updates to Windows that had occured then would be discarded.  Proceed.  An hour and a half later I'm back up and voila!  I can open my old pdf files.  I hope this helps.  I have to say that neither Adobe, Inc., nor Microsoft, Inc. participated in the solution to this problem.  My sympathy goes out especially to business people who have suffered from similar problems.  It seems that we users should be getting more help than we are.  How about a really good TROUBLESHOOTER?  You know, like press the button and it's fixed?

I really hope I'm not back in a day or two (or an hour or two) reporting that the problem has recurred.