Is there a way to stop MS Word from automatically opening previously opened documents?
From the macrumors forums you can hold shift when you launch a program to launch it without the resume previous window functionality.


  Alternatively, for those who want some resume functionality and don't
  want to globally disable it, you can hold Shift when you launch an
  application to bypass resume and start that app fresh.


If that doesnt work you can turn off the function globally by going to System Preferences -> General and unticking "Restore windows when quitting and reopening apps"

(you can also disable the function on a per-app basis using the instructions here)