is it possible to fade the vocals in a song so music is loud and words are quiet
You can try the [u]Vocal Remover[/u] or [u]Vocal Reduction and Isolation[/u] effects.
Note that these effects use “tricks” that assume the vocal is in the center (identical in both channels) and that there is non-centered stereo music. Your results will vary depending on the recording, but you rarely get “professional” results. (You can totally remove all of the centered sounds.)
…“You can’t un-bake a cake or un-fry an egg, and you can’t un-mix audio.”