How to add an underlay object?

[rtejada]

Hi everybody,

I have not found an .net sample showing the way to add an underlay object as an xref.
For instance, a raster image COM object have the addRaster method like

dim acadDoc as AcadDocument = myAcadApplication.ActiveDocument
dim rasterObj as AcadRasterImage
rasterObj = acadDoc.ModelSpace.AddRaster(........

Similarly a dwg xref have the AttachExternalReference method.

Any hint on how to add an underlay (dwf, dgn or pdf) as xref will be appreciated.

Thanks