How do I place new content underneath all of the existing items on a PDF page?

Q: I want to take 2 random images and place them underneath all of the
existing items on a pdf.

How would you do this? Do you have a sample? I am able to insert an
image with opacity, but I need the other objects to draw in top of it.
(a Z-order function?)
A: To insert new content behind all existing content on PDF page pass
‘true’ as the second parameter in the call to writer.Begin(page,
false) method. For example:

  PDFDoc doc = new PDFDoc("my.pdf");

  ElementBuilder eb = new ElementBuilder();
  ElementWriter writer = new ElementWriter();

  // Get the first page
  Page page = doc.GetPage(1);

  // Begin writing to the page
       // (as a background layer). To write in foreground remove
       // the second parameter.
  writer.Begin(page, true);

  // Begin writing a block of text
  Element element = eb.CreateTextBegin(
       Font.StandardType1Font.e_times_roman), 12);

  string txt = "Hello World!";
  element = eb.CreateTextRun(txt);
  // Scale-up text 5 times and shift it by (0,600)
  element.SetTextMatrix(5, 0, 0, 5, 0, 600);

  // Set the spacing between lines

  // Draw the same text string; this time stroked.
  element = eb.CreateTextRun(txt);
  GState gstate = element.GetGState();

  // Finish the block of text

  doc.Save("out.pdf", 0);
catch (PDFNetException e) {