Have you typed in an entry? The Add button doesn't activate until there is
something new too be added. IOW, enter something into the Replace: box,
enter something into the With: box & the Add button will spring to life.
If you're not finding this to be the case please indicate what exactly you
are doing & what specifically is/is not happening. Also include your version
information for Word/Office as well as OS X & what type of Mac.
HTH |:>)
Bob Jones
[MVP] Office:Mac