Function ChangeFont(oDoc As Document) As Boolean
Dim oStory As Range
    On Error GoTo err_Handler
    For Each oStory In oDoc.StoryRanges
            With oStory.Find
                .Font.Name = "Arial"
                Do While .Execute
                    oStory.Font.Name = "Trebuchet MS"
                Loop
            End With
        If oStory.StoryType <> wdMainTextStory Then
            While Not (oStory.NextStoryRange Is Nothing)
                Set oStory = oStory.NextStoryRange
                With oStory.Find
                    .Font.Name = "Arial"
                    Do While .Execute
                        oStory.Font.Name = "Trebuchet MS"
                    Loop
                End With
            Wend
        End If
    Next oStory
    Set oStory = Nothing
    ChangeFont = True
lbl_Exit:
    Exit Function
err_Handler:
    ChangeFont = False
    Resume lbl_Exit
End Function