pdf files will not open in Acrobat Reader on pc

"There was an error opening this document. The file is damaged and could not be repaired." That is the error message when trying now to open downloaded pdf files in Acrobat Reader (64-bit latest version) on my pc with Windows 10. Older pdf files open fine. The problem files in question can be opened with Microsoft Edge browser, so the files appear to be ok. What is wrong, and what do I do to fix this??