2017-11-14 21:37 AEST by Arthur Barrett - Here is a thread about approaches to comparing PDF's that would work for xdiff:
https://stackoverflow.com/questions/11004524/how-to-compare-two-pdf-files-through-command-
line#11773622

ComparePDF:
http://www.qtrac.eu/comparepdf.html

It relies onPoppler - a PDF rendering library based on the xpdf-3.0 code base.
https://poppler.freedesktop.org

It also relies on qt:
https://www1.qt.io/buy-product/

xpdf-3.0:
http://www.foolabs.com/xpdf/