For example:
Sub Insert_Lines()
Application.ScreenUpdating = False
With Selection
  With .Find
    .ClearFormatting
    .Replacement.ClearFormatting
    .Wrap = wdFindStop
    .Text = ""
    .Replacement.Text = "^p^&"
    .Font.Bold = True
    .Execute Replace:=wdReplaceAll
  End With
End With
Application.ScreenUpdating = True
End Sub