Viewer not displaying PDF files

I had to remove adobe reader due to some outside interfearince, I have re installed it, but the viewer no displays file contents, v saying it needs adobe reader which I have installed how do I get it working,PLEASE its a BIG deal?

Does File Explorer's viewer show them?

No it does not, I had some computer issues and may have deleted a nesessary file need to do this, what would it be, I tryed installed adobe reader? PLEASE I need help.

File Explorer viewer does not show them either

Edge (Chromium) can be used for PDF viewing on most Windows versions. You can switch to using that in the viewer pane for PDF by configuring the MetaPlugin in Opus and disabling the PDF preview handler (Adobe Reader or similar in your case) so that the PDF extension falls through to the Edge item lower down the list.

If you don't want to use Edge or another PDF viewer and need to repair Adobe Reader, you may need to ask Adobe for support, since it's not part of Opus.