Adobe 8

Also, moving this to the Acrobat Reader forum, which is the more appropriate forum for your question.

The Using the Community forum is for help in using the Adobe Support Community forums, not for help with specific programs. Product questions should be posted in the associated product community.

Acrobat Reader 8 is really old, and can't open PDF version 1.8 files, although it can open up to PDF 1.7.

Edited to add: As of Catalina, Macs do not run 32-bit applications, and I think that Reader 8 is definitely in that category. 

Why use such an old version, anyway? You can download the latest version of Acrobat Reader DC (still free), which is available here: https://get.adobe.com/reader/