This class represents the file attachment annotation. This is definitively detailed in:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 184, page 406.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 187, page 492.

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.FileAttachmentAnnotationElement

A file attachment annotation embeds a file at a specific page location represented by an icon. The FS entry references the embedded file specification. The Name entry selects the icon style.