MS Windows 10 File Explorer can't search names of any PDF files.

I havedownload thousands of PDF files to various folders on my Win 10 desktop computer over the years. Recently I used File Explorer to find a certain file & it said "no items match your search". This seems to only be for PDF files as other extensions are able to be found. I have been in contact with MS Tech support. They can't find a solution. They re-indexed my hard drive and now I can't search for hardly any of my files. They are present & readable but can't be found in search box. They say it's a problem with PDF files hidden or corrupted. After the MS tech finished messing with settings it seems to be worse. I use acrobat reader DC to open files & they open up just fine. I don't have a paid version. Is there any way to find out what has happened? MS says it's an adobe problem.