It is illegal to use any passport that has been falsified, especially if it is used to obtain work or for travel. It is illegal to use a copy of a foreign passport or make a copy of a foreign passport or any passport for that matter if items that are for identification are falsified. If you know someone who has used this for major or minor acts, you may wish to inform the proper authorities. Since the question is very broad, those authorities can be anyone from the police to teachers to immigration if that is the issue or even the FBI if there was a major cross jurisdictional crime committed.