Quindi la soluzione:
codice:
Function WordConv(wrd As Word.Application, fileInput As String, fileOutput As String, tipo_oggetto As Long)
    Dim wrd_doc As Word.Document
    Set wrd_doc = wrd.Documents.Open(fileInput)
    wrd_doc.SaveAs fileOutput, tipo_oggetto
    wrd_doc.Close
End Function

Function ApriWordApp() As Word.Application
    Dim wrd As Word.Application
    Set wrd = CreateObject("word.application")
    Set ApriWordApp = wrd
End Function

Function ChiudiWordApp(wrd As Word.Application)
    wrd.Quit
    Set wrd = Nothing
End Function
...Elaborazione terminata in 2 minuti, grazie mille ancora.