This .NET class wraps the AcDbDgnReference ObjectARX class. 

Represents DGN underlays in the drawing. Underlays are similar to raster images but their content is snappable.

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.Entity
        Autodesk.AutoCAD.DatabaseServices.UnderlayReference
            Autodesk.AutoCAD.DatabaseServices.DgnReference

Public Class DgnReference
Inherits UnderlayReference

public class DgnReference : UnderlayReference;