Problem with Server.MapPath

Hello everybody.
I'm writing a class and I get a red squigly underline under the word "Server" in the following snippet.  When I hover the mouse over the word "Server" the messages says: "The name 'Server' does not exist in the current context".  Can somone please help me with this?
 
using System;
using System.Collections.Generic;
 using System.Linq; using System.Web;
 using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
namespace FirstPDFtest {    
    public class ClassPDF    
        {        
            public void CreatePDF()         Go to the complete details ...