Cool post to find the Filename portion of a path that includes the filename. Simply replace zFilename in two locations in the example below with the name of your user defined variable name. This user defined variable must contain the full path including the filename. Create another user defined variable to store the filename portion of the string, then assign it this expression:
REVERSE(SUBSTRING(REVERSE( @[User::zFilename] ), 1, FINDSTRING(REVERSE( @[User::zFilename] ),"\\", 1)-1))
Works a treat!