I cannot run your comparison example program asserts at bold line below, message is:
Thank you for giving a try to GroupDocs.Comparison API.
We are sorry to hear that you are facing such issue. There are trial limitations on unlicensed API therefor you are not getting Pdf Comparison.
“PDF documents: document should not have more then four elements of any collection”
click here to see more details for trial limitations.
There is another reason for not getting Pdf comparison results which is if you are using our GitHub example to test API in trial mode kindly comment out all other Document comparison in program file as it is also generating more than 15 comparison results and Pdf comparison comes after 15 files so it is another factor which may be restricting you to compare Pdf files.
Thank you for your patience.