I can't test the way you describe, because I have both Word 2003 & Word 2010 installed on my system and automation starts Word 2003. However, the following should resolve the issue:
Code:
Dim WW
Dim FileName
Dim SaveFormat
SaveFormat = 0
FileName = "C:\tmp\sample."
FileCopy FileName & "doc", FileName & "rtf"
Set WW = CreateObject("Word.Application")
WW.Visible = True
WW.Documents.Open FileName & "rtf"
Call WW.ActiveDocument.SaveAs(FileName & "doc", SaveFormat)
WW.ActiveDocument.Close False
Kill FileName & "rtf"