The author of ExamDiff Pro answered in the forum, suggesting using the catdoc plug-in. This is what worked for me:
Name: Rich Text Format [installed]
Application: cmd /c C:\junk\EXAMDI~1\Plug-Ins\catdoc\catdoc.exe
Original author of catdoc is Vitus Wagner
but his page only has Unix and DOS versions: Free Software Directory page is here
. I suspect I had to use SFNs because catdoc doesn't support LFNs.
@fenixproductions: I vaguely knew about WinMerge, but found this
WinMerge is decent, but go with pretty much any of the others instead of it.