He couldn’t avoid church music, but that doesn’t mean he had to totally embrace it. Writing the score for Edward Berger’s thriller “Conclave,” set inside the Vatican during the election of a new pope, composer Volker Bertelmann knew that any film that takes place within those walls would have to find a way to nod to the sound of ecclesiastical music over the centuries. “It absolutely needed to be part of it,” said the German composer. “This is one of the oldest places in Christianity, and the seat of power and mystery. I wanted to find music that was reflecting the holy halls. And obviously, the first thing you might want to do is use a choir or organ music.”

But Bertelmann, who has worked in the fields of hip-hop and classical music as well as almost two dozen albums of his often experimental compositions, didn’t...