I have downloaded a couple of zip files, and am trying to use the default Archive utility to unzip them. Instead of opening the files within the zipped folder I'm getting a .cpgz folder with the exact same name... then when I try to open that file it makes a duplicate .zip folder and I just go in circles.
Unfortunately nothing in that whole conversation helped. I tried to download a few other applications and none of them worked. The renaming of a .zip file to a .pptx file doesn't make any sense at all. I appreciate the help, but can't find an answer.
Go to http://www.stuffit.com/mac-expander.html and download the free Stuffit Expander. Once it's on your machine, drop a zip file onto it, and see if it expands. That will eliminate some possible broken items.
I would say your archives are damaged. I always get .cpkg files when I try to unarchive an invalid zip file.
maybe another application is able to open them, but I would guess not