Here is a VB example based on what was posted by Albert Szilvasy.
<CommandMethod("BlkTest")> _
Public Sub blkTest()
Dim doc As Document = Application.DocumentManager.MdiActiveDocument
Dim ed As Editor = doc.Editor
Dim tr As Transaction = doc.TransactionManager.StartTransaction
Try
Dim dwgName As String = HostApplicationServices.Current.FindFile("C:\temp\myLines.dwg", Application.DocumentManager.MdiActiveDocument.Database, FindFileHint.Default)
Dim db As Database = New Database(False, False)
db.ReadDwgFile(dwgName, IO.FileShare.Read, True, "")
Dim NewBlkId As ObjectId
NewBlkId = doc.Database.Insert(dwgName, db, False)
Dim bt As BlockTable = tr.GetObject(doc.Database.BlockTableId, OpenMode.ForRead, True)
Dim btr As BlockTableRecord = tr.GetObject(bt(BlockTableRecord.ModelSpace), OpenMode.ForWrite, True)
Dim bref As BlockReference = New BlockReference(New Point3d(0.0, 0.0, 0.0), NewBlkId)
btr.AppendEntity(bref)
tr.AddNewlyCreatedDBObject(bref, True)
tr.Commit()
Catch ex As Exception
ed.WriteMessage(ex.ToString)
End Try
End Sub