Sub ConvertFiles()
Application.ScreenUpdating = False
Dim strFolder As String, strFile As String, wdDoc As Document
strFolder = GetFolder
If strFolder = "" Then Exit Sub
strFile = Dir(strFolder & "\*.doc", vbNormal)
While strFile <> ""
  If InStrRev(strFile, ".docx") = 0 Then
    Set wdDoc = Documents.Open(FileName:=strFolder & "\" & strFile, _
      AddToRecentFiles:=False, Visible:=False)
    wdDoc.SaveAs2 FileName:=strFolder & "\" & Left(strFile, InStrRev(strFile, ".doc")) & "docx", _
      Fileformat:=wdFormatXMLDocument, AddToRecentFiles:=False
    wdDoc.Close SaveChanges:=False
  End If
  strFile = Dir()
Wend
Set wdDoc = Nothing
Application.ScreenUpdating = True
End Sub
 
Function GetFolder() As String
Dim oFolder As Object
GetFolder = ""
Set oFolder = CreateObject("Shell.Application").BrowseForFolder(0, "Choose a folder", 0)
If (Not oFolder Is Nothing) Then GetFolder = oFolder.Items.Item.Path
Set oFolder = Nothing
End Function