This sample shows how to create bookmarks.
Bookmarks are called outlines in the PDF reference manual, that's why you deal with the class PdfOutline.

A screen shot for the Bookmark sample (click image to enlarge):

Bookmarks

// Create a new PDF document
PdfDocument document = new PdfDocument();
// Create a font
XFont font = new XFont("Verdana", 16);
 
// Create first page
PdfPage page = document.AddPage();
XGraphics gfx = XGraphics.FromPdfPage(page);
gfx.DrawString("Page 1", font, XBrushes.Black, 20, 50, XStringFormat.Default);
 
// Create the root bookmark. You can set the style and the color.
PdfOutline outline = document.Outlines.Add("Root", page, true,
  PdfOutlineStyle.Bold, XColors.Red);
 
// Create some more pages
for (int idx = 2; idx <= 5; idx++)
{
  page = document.AddPage();
  gfx = XGraphics.FromPdfPage(page);
 
  string text = "Page " + idx.ToString();
  gfx.DrawString(text, font, XBrushes.Black, 20, 50, XStringFormat.Default);
 
  // Create a sub bookmark
  outline.Outlines.Add(text, page, true);
}
 
// Save the document...
string filename = "Bookmarks.pdf";
document.Save(filename);
// ...and start a viewer.
Process.Start(filename);