(... ) which he loses in some kind of situation where he refuses to help another man. The man he refuses to help is fighting for his child custody after his ex-wife decided to move out of the city, and the fact that the first man didn't help him makes him be late for the custody's judgment, making him lost the case. After this the man then notices he got that document, the one the business man loose, and tries to blackmail him because he refused to help and made him lost custody of his child.

Additional:
*The business man tries to falsify the document at some point of the movie.
*As far as I remember, the second man gets back with his wife at the end.
*Sorry for bad english.

Changing Lanes. With Ben Affleck & Samuel L.Jackson