Thank you for the response. I was definitely not comparing a .doc to a .pptx. The two files in the Zip folder fail on their own during any Compare process.
Thanks for the clarification. Yes, you are right, GroupDocs.Comparison cannot open these two files “Standard Invoice 2 - 006j0000002cSzy.doc” and “Standard Invoice 2 - 006j0000002cSzy.pptx”, which can be found in the ZIP archive. We are able to reproduce this exception, it seems that this is a bug inside a GroupDocs.Comparison. The development team is already notified and working on it, when there will be any news about this issue, we will notify you in this forum thread.
Thanks and sorry for the inconvenience.