Rect box = stamp_annot.GetRect(); Matrix2D m = first_page.GetDefaultMatrix(); double x1=box.x1, y1=box.y1; m.Mult(ref x1, ref y1); double x2=box.x2, y2=box.y2; m.Mult(ref x2, ref y2); first_page.SetCropBox(new Rect(x1, y1, x2, y2));