Adds a text annotation: a note shown as an icon in rect, whose text a viewer shows when it is opened.
public PdfTextAnnotation AddTextAnnotation(PdfRectangle rect, string text, PdfAnnotationOptions? options = null)
The icon's rectangle in default user space.
The note's text (Contents).
Colours, flags and markup texts; null for the defaults (a yellow icon).
ISO 32000-2 §12.5.6.4, Table 175 (Name Note).