The Texas Single Member LLC is a legal document specifically designed to be used by a single owner of a business that helps justify their agreement between themselves and the company. In addition, the owner has the opportunity to define fundamental operations and guidelines for his business. This document offers advantageous tax options as soon as the document has been submitted to the state. A PLLC company agreement is a legally valid document used by PLLC or professional limited liability companies to define the internal rules governing PLLCs. A LLC differs from an LLC in that it is only transactions involving certain professions that require a license to carry on an activity, such as law, medicine and accounting.