How to modify the iTextSharp DLL so Gridviews are rendered with background color

I found your tutorial online at http://www.aspsnippets.com/Articles/Export-GridView-To-Word-Excel-PDF-CSV-Formats-in-ASP.Net.aspx  and it helped me finally understand how to send content from a page to a .pdf .

In your tutorial you mention that you modified the iTextSharp Library DLL so the gridview would be rendered with all the background colors.   Can you you explain how to modify that DLL.  I really want my gridviews to all go to pdfs with pretty formatting, but can't figure out how or what to change?  

The output in your sample is great, and would love to use it as a starting point to modify my gridviews.