Using the latest sample front end here:
Thank you for the detailed information and your anticipation.
We will further investigate on GroupDocs.Annotation for .NET showcase example and will share our findings. However above mentioned front-end is open source and you can also modify it as per your requirements if you want.
Thank you for your cooperation.
We are glad to inform you that GroupDocs team has launched an other exciting front-end example for our customer with simplified code and latest UI. Please click here to explore the new front-end to avoid issues and difficulties with old front-end.
If you will need any help or you will have any other questions regarding GroupDocs.Annotation for .NET API please feel free to ask.