This class represents the external data dictionary. This is definitively detailed in:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 170, page 391.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 332, page 695.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 173, page 477.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 8.21, page 38.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 9.39g, page 76.

System.Object
    WebSupergoo.ABCpdf14.Elements.Element
       WebSupergoo.ABCpdf14.Elements.ExternalDataElement
          WebSupergoo.ABCpdf14.Elements.D3DAnnotationExternalDataElement


An external data dictionary stores a reference to a 3D artwork resource for a 3D annotation, separating the annotation dictionary from the heavyweight 3D stream.

The Subtype entry identifies the kind of external data. In current use only 3D data is defined as a subtype.