Hi,
As far as I know, we can't complete this scenario with field. And we might do it via some Active x controls and VBA code.
If you need help about coding, I recommend you post the question to MSDN forum:
http://social.msdn.microsoft.com/Forums/en-US/home?forum=worddev&filter=alltypes&sort=lastpostdesc
The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with us.
George Zhao
TechNet Community Support