I need to authenticate documents which are executed in the United States and will be used in China.

I need to authenticate a Certificate of Free Sale & Good Manufacturing Practices (for business) but your webpage says: "You may come to the relevant Embassy or Consulate Generals for application, or send a representative to apply for you. No appointment is required. Mailed applications are not acceptable and will be returned." I am located in Florida (this jurisdiction belongs to CHINESE HOUSTON EMBASSY). There is a way to send them by mail (MAYBE FEDEX?) instead to apply in person? Thank you, Liz Solis