to read pdf file and then write it using c#

Hello... I am doing one project in which I need to read pdf file and then write it in a textbox.
Can somebody help me??
 
I have used iTextSharp named dll file but it is showing me error in namespace

using System.Web.UI;
using System.Web.UI.WebControls;
using iTextSharp.text.pdf;
using iTextSharp.text.pdf.parser;

How to remove this error? and can you please tell me the code to read a pdf file and then write it to a textbox???
 
[edit] Added code blocks [/edit]