It sounds as if you are using a pre-existing template.
A DOCPROPERTY field just gets a value from the properties you can set in
Word File->Properties. In this case if you go to File->Properties and
click Custom, you may see one or more properties listed, one of which
should be called InvNum.
To change the value you would have to select that property and modify
its value, /then/ go and update the { DOCPROPERTY } field.
The thing is that someone may have put some code (e.g. some VBA code in
the template) that is supposed to increment that property value. Without
such code, nothing would ever change the value of the property, so you
would have to do it manually. So you probably need to ind out what is
/supposed/ to happen in your case.
Peter Jamieson
http://tips.pjmsn.me.uk