No rule for this one
No ending or word group predicts the article of Film. Learn it as a pair and say it out loud: der Film.
der Film
It's der Film. Film is masculine, plural die Filme.
Der Film ist spannend.
The film is exciting.
Wir schauen einen Film.
We are watching a film.
No ending or word group predicts the article of Film. Learn it as a pair and say it out loud: der Film.