Your friend will probably want to know the approximate age of his find. Enlarging the photo indicates your friend's "NAPOLEON SUPEREUR" button's back is one variety of what button-collectors call a self-shank back, and all self-shank backs are from the 20th-Century.
The term self-shank back means the button's back is machine-pressed to form a raised tunnel for the thread to sew the button onto clothing, instead of the shank being a separate piece of metal (such as a wire loop) which is attached to the button's back.
The particular version of self-shank back on your friend's button seems to first show up in the 1940s/50s, and is still being manufactured today. See the photo below.