I cannot comment for Excel,and PP, but for Word the following should do the
trick.

Sub SaveAllAsDOC()
Dim strFileName As String
Dim strDocName As String
Dim strPath As String
Dim oDoc As Document

With Dialogs(wdDialogCopyFile)
If .Display <> 0 Then
   strPath = .Directory
Else
   MsgBox "Cancelled by User"
Exit Sub
End If
End With

If Documents.Count > 0 Then
   Documents.Close SaveChanges:=wdPromptToSaveChanges
End If
If Left(strPath, 1) = Chr(34) Then
   strPath = Mid(strPath, 2, Len(strPath) - 2)
End If
strFileName = Dir$(strPath & "*.docx")

While Len(strFileName) <> 0
Set oDoc = Documents.Open(strPath & strFileName)

   strDocName = ActiveDocument.FullName
   intPos = InStrRev(strDocName, ".")
   strDocName = Left(strDocName, intPos - 1)
   strDocName = strDocName & ".doc"
   oDoc.SaveAs FileName:=strDocName, _
       FileFormat:=wdFormatDocument
   oDoc.Close SaveChanges:=wdDoNotSaveChanges
   strFileName = Dir$()
Wend
End Sub