Place the overlay text 'under' other drawn objects.
[read-only property] overlayUnder([out, retval] LONG *flag)
Draw the overlay text first so that it appears "under" other drawn objects on the page (a so-called watermark). The exact behavior will depend on the nature of the PDF file: for example, a PDF file that starts by drawing a large, white, filled rectangle over the entire page will cover up any overlays drawn with this flag.

This property is only useful as an argument to the addOverlayText function.

pdf.addOverlayText "CONFIDENTIAL", "Arial", 1, 0, "Helvetica-Bold", _ RGB(0, 0, 0), 10, 200, 50, 0, pdf.overlayUnder