Hello, to manage how to view your PDF files, I recommend you visit the following link and carry out the procedures detailed there, one of them may help you solve your problem. View PDF files in Firefox or choose another viewer

I appreciate your response, but as I indicated I have already done most of this. Adobe Acrobat is set to be my PDF reader, however, Offidocs opens anyway. I would like to avoid refreshing Firefox so I don't have to go thru the process of re-installing all the add-ons. If I completely re-installed Firefox what would that entail and what steps would I need to follow to keep Offidocs from re-installing before I can make sure Acrobat is checked again? I never installed Offidocs in the 1st place. It must have come with another program like IrfanView, from an earlier version of Windows 10. Thank you.