How about
Code:
Sub FixMargin()
Dim oDoc As Document
Dim oSection As Section
Set oDoc = ActiveDocument
If oDoc.Sections(1).PageSetup.PaperSize = wdPaperA4 Then
For Each oSection In oDoc.Sections
If oSection.PageSetup.Orientation = wdOrientLandscape Then
oSection.PageSetup.LeftMargin = InchesToPoints(1.8)
End If
Next oSection
oDoc.Save
End If
lbl_Exit:
Set oDoc = Nothing
Set oSection = Nothing
Exit Sub
End Sub