Thank you for your interest in GroupDocs. We checked your requirements and looks like for you it's better to use different viewers / products, since for Comparison if you want to be able to move through the differences, you need to use the Viewer that has been extended to support this. If you don't need that functionality then you can just use GroupDocs.Annotation for .NET after doing the comparison and use the redline version of the result document in GroupDocs.Annotation for .NET. But it really depends on your application and use-case on whether or not you need to use two separate viewers or just one viewer.
About the issue with comparison two documents - we are sorry to hear that you have such issue with comparison in cloud service , but we checked this issue and it works fine for us. Please notify us if you still get this error and please provide your email which you use for comparing documents.
Please notify us if you will have any issues or questions, we will be glad to help you.
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