why ns0?

I created a schema with the following prolog

?xml version="1.0" encoding="UTF-8"?
xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.trp.com"
xmlns:trp="http://www.trp.com"
elementFormDefault="qualified"

My namespace prefix is trp. However, when I create an XML document based
upon this schema Word substitutes the text ns0 for the name space prefix. How
do I enforce the use of trp as the name space prefix in the WordML document?