ESRI.ArcGIS.ArcMapUI.IMxDocument mxd = ArcMap.Application.Document as
                                           ESRI.ArcGIS.ArcMapUI.IMxDocument;
            ESRI.ArcGIS.Carto.IMap map = mxd.FocusMap;
            ESRI.ArcGIS.Geodatabase.IWorkspaceFactory wsf = new ESRI.ArcGIS.DataSourcesGDB.FileGDBWorkspaceFactory();
            ESRI.ArcGIS.Geodatabase.IWorkspace ws = wsf.OpenFromFile(@"D:ARC OBJECTSTemplateData.gdb", ArcMap.Application.hWnd);
            ESRI.ArcGIS.Geodatabase.IFeatureWorkspace fws = ws as ESRI.ArcGIS.Geodatabase.IFeatureWorkspace;
            ESRI.ArcGIS.Geodatabase.IFeatureDataset fd = fws.OpenFeatureDataset("World");

            ESRI.ArcGIS.Geodatabase.IFeatureClassContainer featureClassContainer = (ESRI.ArcGIS.Geodatabase.IFeatureClassContainer)fd;
            ESRI.ArcGIS.Geodatabase.IFeatureClass newFeatureClass = featureClassContainer.get_ClassByName("World");
            ESRI.ArcGIS.Carto.IFeatureLayer flay = new ESRI.ArcGIS.Carto.FeatureLayerClass();
            flay.FeatureClass = newFeatureClass;

            mxd.AddLayer(flay);