How to append a page to existing pdf using asp.net

Hi ,
 
How to append a page to existing pdf using asp.net,
 
i used the following code with Visual studio 2005.
 

Document doc = new Document();
doc.NewPage();
 

 
but old page is replacing with new content.But i need just append of data to existing pdf,i.e if the pdf contains 2 pages,if i want to add the data then 3rd page should be created and content should be fall in 3rd page only.