This class represents the rubber stamp annotation. This is definitively detailed in:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 181, page 405.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 184, page 490.

This class is always an indirect object because it inherits from MarkupAnnotationElement which is always an indirect object.

System.Object
    WebSupergoo.ABCpdf14.Elements.Element
       WebSupergoo.ABCpdf14.Elements.AnnotationElement
          WebSupergoo.ABCpdf14.Elements.MarkupAnnotationElement
             WebSupergoo.ABCpdf14.Elements.RubberStampAnnotationElement

A rubber stamp annotation displays a text or graphical stamp on the page. The stamp's appearance is defined by a Name chosen from standard values such as Approved, Draft, Confidential, or Experimental.

Viewers render the chosen name as a stylised stamp. If the Name is not recognised the viewer renders the AP entry or falls back to a default rendering.