The movie's subject, Henri Langlois, may be unknown to many -- though it's a name any movie-lover should revere. Langlois, born in Turkey, was the longtime director of the Cinematheque Francaise, which he founded in 1936 (with filmmaker Georges Franju), nurtured under great difficulties through WW II and brought to world prominence in the '50s.
Langlois decided, initially without government aid, to assemble a film library. At first he did it selectively, preserving what conventional wisdom considered the classics. But after he let a print of actress Theda Bara's silent "Salome" get away (a film now lost forever), he decided that conventional wisdom might be wrong, that it was best to try to preserve and show as much as possible. The official critical establishment might have missed some classics.
Indeed. And here is a gratuitous Theda Bara photo, I believe in the role of Salome: