I downloaded GroupDocs.Viewer-for-.net-master from the github website and ran the Demo inside GroupDocs.Viewer-for-.net-master\Demos\ASP.net MVC\src. When previewing dwg, execute the LoadDocumentDescription method
var d…...Viewer-for-.NET Can't preview dwg file GroupDocs.Viewer...downloaded GroupDocs.Viewer-for-.NET-master from the github website...