Forgery, deceive or injure another, he falsely makes, completes or alters a written instrument which is or purports to be. The law of Forgery in New York does not place any more emphasis on falsely making, altering or completing a written instrument.Your knowledge of the fact that the document is forged can be established by:. A written instrument can be either complete or incomplete. Facing forgery charges? Michael A. Arbeit, PC offers defense for forgery offenses in NY and Long Island. Forged documents can range from checks and wills to prescriptions, contracts and even art.