We are sorry for the trouble. As described you get the bad parameter error when you compare the PDFs?
We need some more information for a better understanding:
Is this a behavior with a particular set of PDF documents or with all the PDFs that you compare? Please try with a different PDF file and check.
What is the version of the Acrobat DC you are using? To check the version go to Help > About Acrobat DC and make sure you have the latest version 20.12.20048 installed. Go to Help > Check for updates.
Do you have Windows or Mac OS?
Have you created the PDF files or have you got them from a different user? Please try to print the PDFs as Adobe PDF and then save them with new file name and then try to compare these new files and check if that works for you.