I\'ve created some annotations (Underline, Highlight, Strikeout, Squiggly) in Acrobat and am digging out the QuadPoints array to render with. The pdf spec PDF 32000-1:2008
I've written a PDF annotation lib for iOS and found the same against-the-spec Acrobat behavior.
As a bit of further info, the Text Markup annotation also contains an Rect entry as well as the QuadPoints entry. The Rect entry is per the spec, [llx, lly, urx, ury]. So in Acrobat generated Text Markup annotations, the Rect point (llx,lly) is approx the same as the QuadPoints point (x3, y3) when rotation=0. Go figure.
Interesting the amount of time that can be wasted when the primary company behind a spec writes software that doesn't follow that spec!