The feature is disabled by default in reader 9
(1) Open Adobe Reader
(2) Click Edit > Preferences > Search, and
(3) check the box labelled Enable search highlights from external highlight server.
(response found here: http://support.dtsearch.com/dts0117.htm)
I can't imagine why Adobe choose to disable it. It's a bad joke for us at UNESCO (http://unesdoc.unesco.org)