Sub Document_Open()
    If ActiveDocument.Sections.Count > 1 Then Exit Sub

    Selection.EndKey Unit:=wdStory
    ActiveDocument.Range(Start:=Selection.Start, End:=Selection.Start). _
        InsertBreak Type:=wdSectionBreakNextPage
    Selection.Start = Selection.Start + 1

    With ActiveDocument.Range(Start:=Selection.Start, End:=ActiveDocument. _
        Content.End).PageSetup
        .LeftMargin = CentimetersToPoints(2.54) 'CHANGE THIS it's margin of new pages!
        .SectionStart = wdSectionNewPage
    End With
End Sub