You could try using the Filter and Substitute functions, allowing only lower case letters, then truncate. So the calculation in your Set Variable step could look something like:
Let ( [ fullName = Lower ( Committee Name ) ;
subName = Substitute ( fullName ; "committee" ; "" ) ;
filterName = Filter ( fullname ; "abcdefghijklmnopqrstuvwxyz" ) ;
shortName = Left ( filtername ; 14 ) ] ;
shortName & ".pdf" )
That calculation steps you through the process: convert to lower case, remove the word "committee" from the lower case version, remove any non-alphabetic characters and then truncate at 14 characters long. Finally it adds the ".pdf" extension. If you have FileMaker Pro Advanced, you could define a Custom Function with a text parameter to do it for you.