When DWO is in preview mode, it looks fine on the screen. It prints fine too.  When savedas PDF! using the nativePDF! apporach, the resultant PDF introduces extra blank pages.

dw_Main.Modify("Datawindow.Export.PDF.Method=NativePDF!")
dw_Main.Modify("Datawindow.Export.PDF.CustomSize = 5")
//dw_Main.Modify("Datawindow.Print.Margin.Left = 75")
//dw_Main.Modify("Datawindow.Print.Margin.Right = 2000")
li_rc = dw_main.SaveAs(ls_pathname, PDF!, FALSE)

As indicated above, i can change the margins at runtime, but knowing what the value should be is a crap shoot.  if is set teh left marging to 75 it look aproximatly what the report will look like when printed.