Post Get Http (URL)

Hi to all, I'm having a problem when I want to convert my Datatable to PDF. I'm using the ephtmltopdf.dll. The problem is that when I click the button to convert to pdf my data has been erased because it makes a refresh page and the pdf page appears with the logo and labels without information. I've been told that I need to use a Post(url) to this to work but don't know how. This is my complete code where the pdf button is how can I make a post and where I have to insert it so it doesn't erase my data.

using System;
using System.Data;
using System.Data.OleDb;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using Dundas.Charting.WebControl;
using ExpertPdf.HtmlToPdf;
using System.Drawing;
using System.Net;

public partial class _Defa ...