If you are using the Close Document button, (below the big red x) then Word
shouldn't close. If you've narrowed it down to documents received from one
individual then it could be a macro is in the document that is either
intercepting the Close command and also exiting the application.
If you don't know how to disable macros, either go to Tools/Macro/ Macro
Security and set macro security to Medium. Exit Word and restart. Then try
opening a document that exhibits the behavior. If you're prompted to enable
macros when you open the document then that indicates it contains macros and
the likely cause of the problem. Click the Disable button and see if Word
exits when you close it.
Also note if macro security is set to High then you won't encounter the
prompt to enable macros, they'll automatically be disabled, which might
explain the difference between the computers
~~~~~~~~~~~~~~~
Beth Melton
Microsoft Office MVP
https://mvp.support.microsoft.com/profile/Melton
What is a Microsoft MVP?
http://mvp.support.microsoft.com/gp/mvpfaqs