Gets the quadrilaterals that enclose the marked-up text (QuadPoints, required), as stored; empty when absent.
public IReadOnlyList<PdfQuadrilateral> QuadPoints { get; }
ISO 32000-2 §12.5.6.10, Table 182. Counterclockwise, with the text along the edge from the first point to the second; written in other orders too (PdfQuadrilateral).