what's the film playing in clement hotel in Ready or Not (Sins of the father)

Charade (1963)

And fun fact - the movie itself is public domain, however the soundtrack is not! We actually had to do some clever editing to add in something non-copyrighted behind the dialogue.

Just reading the wiki page for it, it looks like because they (accidentally?) omitted adding a copyright notice somewhere during the film’s runtime, essentially making it public domain the second it released

Now the soundtrack is a different story, because it was copyrighted by a key contributor or their estate, that remains protected outside of the context of the movie.

So technically, we could’ve used the original soundtrack, but just playing it safe 😉

https://en.m.wikipedia.org/wiki/Charade_(1963_film)