If you just leave the 'replace' section blank, it will remove the matched text.
The regex that you need depends on what's in your PDF. Pulling page numbers is different than removing path information.
Since the stuff you want to get rid of is usually on one line, you can use pretty simple regexes like:
file:///F|/rah/Author%20D.%20Writerperson%20Title%20Book.txt (1 of 105) [1/14/03 10:48:52 PM]<br>