How to get XGraphics class in PDFsharp

I am using PDFsharp to generate pdf, but I cannot use the XGraphics class. Can someone tell me how can I use the XGraphics class or what is the dll and namespace that I need to add to my application. Actually I need to draw a line in the header and footer of my dll and from the link http://www.pdfsharp.net/wiki/Graphics-sample.ashx#Draw_simple_lines_0 there is a DrawLine () method which using the XGraphics class which I I can not find.