From what I have seen, and come to understand, the only sure fire way to do this is to iterate through the running instances of word and then kill each one in turn to be sure that you are getting the next instance.
Since word registers in the running object table the same exact way for every instance of itself, there is no way to get through them without first closing the one you were looking at.
One option to this approach, which is probably not desirable, is to get all the file names while you are killing the application instances and then load them all back in one instance that you create.
Alternately if you know the names of the open files, you can 'getObject' by open file name since Word will push its document names into the running object table, sadly this does not sound like the case for you.
Without writing an active x MFC service, you are not going to be able to do what you are looking to do.
I hope that is helpful.
EDIT:
there was an extensive discussion on subclassing and windows API's to get handles in order to change focus. http://www.xtremevbtalk.com/showthread.php?t=314637
if you dove into that head first and were able to enumerate the word instances by hwnd then you could potentially focus each one in turn and then list the file names. I do warn you though; that is some nasty subclassing which is dark magic that only some people who really want to accidentally break stuff play with.
In any event if you wanted to take the look at one instance, kill, repeat, reopen try this:
Adapted from this thread: http://www.xtremevbtalk.com/showthread.php?t=316776
Set objWordApplication = GetObject(, "Word.Application")
'//clear combobox
OpenDocs.Clear
'//add all open documents to combo box
Do While Not objWordDocument is nothing
For Each objWordDocument In objWordApplication.Documents
OpenDocs.AddItem objWordDocument.Name
Next objWordDocument
objWordApplication.Quit False
Set objWordApplication = Nothing
Set objWordApplication = GetObject(, "Word.Application")
loop
** use create object to open a new instance of word here and then go though
** your list of files until you have opened them all as documents in the new
** instance.
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