My 2019 Return PDF will not open with a warning that "Adobe Acrobat Reader could not open 'file2019' because it is either not a supported file or it is corrupt…" Fix?

1) double-check the file extension...is it ".pdf" ?  or ".txt' ?  (IF it's ".txt", you can change it to ".pdf" , and it might work, but that depends on whether it's already messed up or not) 

2) if you used the "Edge" browser to download the PDF, try using a different browser to download it...and try again.