Overview of Texas Forgery Laws. Texas forgery law makes it a crime to forge a "writing" with intent to defraud or harm another person.The account holder MUST provide an Affidavit of Forgery before any criminal charges can be filed! An affidavit must accompany each forged or counterfeited item. No, it is not illegal. Forging documents in Texas is a serious crime with severe penalties. Learn about Texas forgery laws, defenses, and possible penalties. A person commits an offense if he forges a writing with intent to defraud or harm another. Signing another's name with permission is not forgery, but be sure that you sign in a way that reveals the permission.