If .dwg files are simalar to .dxf files then part of your problem may be with the parameter you are providing for
Input_Features, i.e. the path to your .dwg file.
I perform the same geoprocessing operation
ESRI.ArcGIS.ConversionTools.FeatureClassToShapefile on .dxf files. Because the .dxf file contains subsets of data within it (i.e. an annotation layer, geometry layers, etc.) you will need to add the sub dataset name to your path. In my case I have .dxf files that have the following sub datasets:
Although these are contained in the same .dxf file they are essentially different datasets so to export the Point data I would need append Point to the
Input_Features parameter to run
ESRI.ArcGIS.ConversionTools.FeatureClassToShapefile like this:
//create geoprocessor object, FeatureClassToShapefile object, and set input parameters
ESRI.ArcGIS.Geoprocessor.Geoprocessor GP = New ESRI.ArcGIS.Geoprocessor.Geoprocessor();
ESRI.ArcGIS.ConversionTools.FeatureClassToShapefile FCToShapeFile = new ESRI.ArcGIS.ConversionTools.FeatureClassToShapefile();
FCToShapeFile.Input_Features = "C:\CAD_to_Shp\temp.dxf\Point"; //appended Point to the path to input features
FCToShapeFile.Output_Folder = "C:\CAD_to_Shp\";
//run geoprocessor operation
**Because this is a standalone application make sure you have taken the steps that @MichaelMiles-Stimson has suggested to initialize the ESRI license.