This class represents the 3D reference dictionary. This is definitively detailed in:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 303, page 519.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 314, page 648.

A 3D reference dictionary links an external 3D annotation to its model data. It is used in the 3D annotation external data dictionary to reference a 3D stream that may reside in a different PDF document.

The 3DD entry holds an indirect reference to the 3D stream dictionary. This reference may point to a stream in the current document or in an externally specified document.

System.Object
    WebSupergoo.ABCpdf14.Elements.Element
       WebSupergoo.ABCpdf14.Elements.D3DReferenceElement