It looks like pure magic. Older versions was released under GPL2 (though the copyright notice contains "All rights reserved" too, tough call), but newer version

It looks like pure magic. Older versions was released under GPL2 (though the copyright notice contains "All rights reserved" too, tough call), but newer versions are under a restrictive license. I wonder how well it works for equations. http://www.qtrac.eu/diffpdf-foss.html http://www.qtrac.eu/diffpdf-foss.html