Thanks for taking interest in GroupDocs.Viewer for .NET.
First of all, I want to brief you a little about how the API works. GroupDocs.Viewer for .NET (starting from version 3.0.0) is a back-end document processing API that renders the supported document formats into either HTML pages or images (as per your choice). You will have to create your own front end application in order to view these HTML pages or images. As it is a back-end API, it does not provide any front end control to view the rendered pages. The API can be integrated in variety of .NET applications (web forms, win forms, web services etc.).
Secondly, yes, GroupDocs.Viewer for .NET supports rendering of fillable PDF documents.
We have also created some sample open source document viewer applications using GroupDocs.Viewer for .NET to demonstrate how the API works with front end applications. You can download, use and modify these applications as per your needs. Listed below are the applications along with the download links.
You can also evaluate all the features of the API one by one using the Examples
project. Some useful resources for getting started with the API are:
If you would have any other questions, please do let us know.