Why can I not convert linear Edges to Lines? Perhaps the name is a bit misleading, but Line in Inventor API represents a straight line with infinite length. It only has a 'RootPoint' and a 'Direction'. In most scenarios, the LineSegment object can do the trick.
Dim oDoc As PartDocument
oDoc = m_inventorApplication.ActiveDocument
Dim oEdge As Edge
oEdge = oDoc.ComponentDefinition.SurfaceBodies(1).Faces(1).Edges(1)
Dim oLineSeg As LineSegment
If TypeOf oEdge.Geometry Is LineSegment Then
oLineSeg = oEdge.Geometry
End If