This .NET class wraps the AcDbDwfReference ObjectARX class. 

Represents DWF 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.DwfReference

Public Class DwfReference
Inherits UnderlayReference

public class DwfReference : UnderlayReference;