Error when "unzipping" powerpoint file using Archive Utility
The way to do it is to either try different unzip utility, such as 7zip, or use terminal: navigate to the folder with your "test.pptx.zip" and run these commands:

mkdir test_dir
cd test_dir
unzip ../test.pptx.zip


First line creates folder test_dir and then moves to that folder. Final command unzips your pptx file into test_dir folder