Forgery, deceive or injure another, he falsely makes, completes or alters a written instrument which is or purports to be. Both forgery and counterfeiting are crimes involving fraud.Forgery is the crime of creating a false written document or object with the intent to defraud. Forgery and fraud offenses are complex, and prosecutors sometimes charge the wrong crime. In essence, forgery is when a person creates a written document under false pretenses. Definition of Forgery. Under our law, a person is guilty of Forgery in the Second. Difference between New York forgery and federal R.I.C.O. statutes.