Hello - this is a fairly easy one, it could be done with calculation stages or regular expressions - there is a section at the end of the interfacing with pdfs guide all about parsing text which may be of use to you, but my suggestion is to experiment with calculation stages, look at the text functions available and use the evaluate expression button until you figure out what you need.
Off the top of my head - how about something like this: Mid([TestText],InStr([TestText],""("")+1,InStr([TestText],"")"")-InStr([TestText],""("")-1)