Thanks for taking interest in GroupDocs.Comparison for Java and posting your concerns. Yes, currently API compares two documents and write out the difference or highlight the style changes to a PDF document.
This is how you can highlight the style change:
ComparisonSettings settings = new ComparisonSettings();
Using this code you can get differences, style changes (with highlighting) and comparison summary in the output document.
However, returning just the information about style changes is concerned, we are investigating this at our end. Your investigation ticket ID is COMPARISONJAVA-445. As we have any update on it, we shall notify you.
You have to purchase GroupDocs.Total for Java or GroupDocs.Comparison for Java license in order to utilize this API.
Please see license types and you can buy license from here. Furthermore, if you have any purchase related inquiry, feel free to post here.