My 5.27.0 runs OK under Windows 7, but command line "?" doesn't work. I tried both wxMaxima and Xmaxima:
Maxima 5.27.0 http://maxima.sourceforge.net
using Lisp GNU Common Lisp (GCL) GCL 2.6.8 (a.k.a. GCL)
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) ? diff;
warning: empty documentation index; ? and ?? won't work!
No exact match found for topic `diff'.
Try `?? diff' (inexact match) instead.
(%o1) false
(%i2) ?? diff;
(%o2) false
(%i3)
--bw