Whether the forged lawyer's letter can be used as evidence depends on what you want to prove. If it is related to the case and needs to be used to prove a certain fact, it can be used as evidence. For example, in economic disputes, it is used to prove that the debtor has been urged to fight the statute of limitations.
A lawyer's letter refers to a professional legal document produced and issued by a lawyer who accepts the entrustment of a client, discloses and evaluates relevant facts or legal issues, and then makes a request to achieve a certain effect.