I am pleased to inform you that the first next generation GroupDocs.Annotation for .NET 3.0.0 is released in the last month. Please have a look at the details in this blog:
Please note that only PDF format is supported in the initial version. More formats are planned to be supported in the future versions. Furthermore, we have released an open source showcase / front end project in ASP.NET MVC. Please feel free to have a look at the details: