Sub RunMailmerge()
Dim sPath As String
'Kill off any previous datasource connections
Application.DisplayAlerts = wdAlertsNone
'Let the user select a datasource
With Application.Dialogs(wdDialogMailMergeOpenDataSource)
  If .Show = -1 Then
    sPath = .Name
  Else
    GoTo NoMerge
  End If
End With
If sPath = "" Then GoTo NoMerge
'Run the merge
With ActiveDocument
  With .Mailmerge
    .MainDocumentType = wdFormLetters
    .OpenDataSource sPath
    .Destination = wdSendToNewDocument
    .SuppressBlankLines = True
    With .DataSource
      .FirstRecord = wdDefaultFirstRecord
      .LastRecord = wdDefaultLastRecord
    End With
    .Execute Pause:=False
    'Disconnect from the datasource
    .MainDocumentType = wdNotAMergeDocument
  End With
  .Saved = True
End With
NoMerge:
Application.DisplayAlerts = wdAlertsAll
End Sub