How would I find paper work for termination of parental rights in the state of Texas?

You are looking for paperwork to terminate your rights?
Or previously filed paperwork?
What leads you to believe that you can?

Parents rights are seldom termnated, normally only when both parties agree and there is a step parent to adopt.
But it will be part of an adoption process.

The non custody parent can not just give up custody in any state without the other parent permission and even then it is almost impossible.

Can you give us more information on this