The standard annotation types, the values of an annotation dictionary's Subtype entry.
public enum PdfAnnotationKind
ISO 32000-2 §12.5.6.1, Table 171. The set is extensible (§12.5.2): any other subtype reads as Unknown.
kind:method, kind:property, kind:ctor. Press Esc to clear.CaretCaret (PDF 1.5, markup): a text insertion point. ISO 32000-2 §12.5.6.11.CircleCircle (PDF 1.3, markup): an ellipse. ISO 32000-2 §12.5.6.8.FileAttachmentFileAttachment (PDF 1.3, markup): an attached file. ISO 32000-2 §12.5.6.15.FreeTextFreeText (PDF 1.3, markup): text displayed on the page. ISO 32000-2 §12.5.6.6.HighlightHighlight (PDF 1.3, markup): highlighted text. ISO 32000-2 §12.5.6.10.InkInk (PDF 1.3, markup): freehand paths. ISO 32000-2 §12.5.6.13.LineLine (PDF 1.3, markup): a straight line. ISO 32000-2 §12.5.6.7.LinkLink (PDF 1.0): a hypertext link. ISO 32000-2 §12.5.6.5.MovieMovie (PDF 1.2; deprecated in PDF 2.0): a movie. ISO 32000-2 §12.5.6.17.PolygonPolygon (PDF 1.5, markup): a closed polygon. ISO 32000-2 §12.5.6.9.PolyLinePolyLine (PDF 1.5, markup): an open polygon. ISO 32000-2 §12.5.6.9.PopupPopup (PDF 1.3): the pop-up window of a markup annotation. ISO 32000-2 §12.5.6.14.PrinterMarkPrinterMark (PDF 1.4): a printer's mark. ISO 32000-2 §12.5.6.20 and §14.11.3.ProjectionProjection (PDF 2.0, markup): a projection annotation. ISO 32000-2 §12.5.6.24.RedactRedact (PDF 1.7, markup): content to be removed. ISO 32000-2 §12.5.6.23.RichMediaRichMedia (PDF 2.0): rich media content. ISO 32000-2 §12.5.6.25 and §13.7.2.ScreenScreen (PDF 1.5): a region where media clips play. ISO 32000-2 §12.5.6.18.SoundSound (PDF 1.2, markup; deprecated in PDF 2.0): a sound clip. ISO 32000-2 §12.5.6.16.SquareSquare (PDF 1.3, markup): a rectangle. ISO 32000-2 §12.5.6.8.SquigglySquiggly (PDF 1.4, markup): text with a jagged underline. ISO 32000-2 §12.5.6.10.StampStamp (PDF 1.3, markup): a rubber stamp. ISO 32000-2 §12.5.6.12.StrikeOutStrikeOut (PDF 1.3, markup): struck-out text. ISO 32000-2 §12.5.6.10.TextText (PDF 1.0, markup): a sticky note. ISO 32000-2 §12.5.6.4.ThreeD3D (PDF 1.6): 3D artwork. ISO 32000-2 §12.5.6.25 and §13.6.2.TrapNetTrapNet (PDF 1.3; deprecated in PDF 2.0): a trap network. ISO 32000-2 §12.5.6.21 and §14.11.6.2.UnderlineUnderline (PDF 1.3, markup): underlined text. ISO 32000-2 §12.5.6.10.UnknownA subtype Table 171 does not list, or no subtype at all: a PdfUnknownAnnotation.WatermarkWatermark (PDF 1.6): content printed at a fixed size and position on the media. ISO 32000-2 §12.5.6.22.WidgetWidget (PDF 1.2): the appearance of an interactive form field. ISO 32000-2 §12.5.6.19.