The RD entry of a free text, square, circle or caret annotation: the distances from each edge of the annotation rectangle
inward to the rectangle where the annotation is drawn.
public PdfRectangleDifferences(double Left, double Top, double Right, double Bottom)
The difference at the left edge.
The difference at the top edge.
The difference at the right edge.
The difference at the bottom edge.
ISO 32000-2 §12.5.6.6 Table 177, §12.5.6.8 Table 180, §12.5.6.11 Table 183 (PDF 1.5). Each difference shall be at least 0.