Is this happening with ALL .pdf files? Have you tried using other PDF readers like Preview, Skim, Libre Office, etc.? If you are partial to Adobe Acrobat Reader, how are you deleting the file before downloading a new copy? You need to first delete other files associated with the app. I would use AppCleaner to accomplish this before running a new copy.
It will also be helpful if you were to specify your macOS setup—what kind of Mac, what version of macOS, etc.