Adds a square annotation: a rectangle drawn inside rect.
public PdfSquareAnnotation AddSquareAnnotation(PdfRectangle rect, PdfAnnotationOptions? options = null)
The rectangle in default user space; the border is drawn inside it.
Border and interior colours, width, flags and markup texts; null for a one-point red border.
ISO 32000-2 §12.5.6.8, Table 180 (PDF 1.3).