This class represents the text field. This is definitively detailed in:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 229, page 444.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 232, page 537.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 8.39a, page 46.

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

System.Object
    WebSupergoo.ABCpdf13.Elements.Element
       WebSupergoo.ABCpdf13.Elements.FieldElement
          WebSupergoo.ABCpdf13.Elements.TextFieldElement