Fonts changing to temp files and symbols

I have always used the arial font for a particular document that I frequently modify and resave as a cover sheet for document packages.  Today when I clicked a text box to edit it in the font selection field it automatically changes to "Z@RE734.tmp" and outputs random symbols when I type.  No matter what I try always when I select ARIAL it does this however arial black and narrow work fine.  I noticed at the bottom of my font list in the drop down there is about 10-15 variations of the the Z file name.  I never noticed that before.  On the fields that currently have arial font text in them, when I click it give the little yellow warning symbol and reports Arial may not be installed.   Any thoughts on what this could be?  I am using Acrobat XI on Win 10 and have been successfully for months.  No new software has been installed and nothing has been deleted.  Before I tried a reinstall of the font, I wanted to ask because there are so many junk font downloads I was a little nervous about doing that.