E.g. I have buttons on my webpage first the user to choose which state they are from. Dependent on which button they click, the fields in the word document will reflect that state.

This seems to have to do with your web page coding rather than Word.
Why not simply use a mapped Content Control in the Word document and let them enter the data there?

• Repeating Data Using Document Properties Content Controls and Other Mapped Content Controls
• Mapped Content Controls by Greg Maxey, MVP
• Insert Content Control Add-In by Graham Mayor, MVP
• Custom Content Control Insert Dialog

The first link uses text content controls built into Word. If you need a drop-down look at the second link and then I would suggest using one of the tools in the last two links. Both easily insert mapped drop-down controls.