What is the section in CA state law?

[arrigo]

What section in CA law says it is illegal to fill in a contract after it has been signed without permission of the signing party? Or what protects the citizen from this happening?

[demarco]

California civil code, sections 1619-1632

It's the same for any state...A contract is a mutual agreement between two or more parties, signed for verification of agreement. If one party changes the terms of the contract without approval of the other party/parties, it's no longer a contract because that portion that was altered was not approved by the co-signers.