How to Export the File in to Pdf, Doc and xls Using Crystal Report

using System;
using System.Data;
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 CrystalDecisions.Shared;
using CrystalDecisions.CrystalReports.Engine;
using CrystalDecisions.ReportSource;
using System.IO;
public partial class _Default : System.Web.UI.Page
{
//protected CrystalDecisions.Web.CrystalReportViewer CrystalReportViewer1;
//protected System.Web.UI.WebControls.Button Button1;
ReportDocument rDoc = new ReportDocument();
protected void Page_Load(object sender, EventArgs e)
{
string FilePath = Server.MapPath("CrystalReport.rpt");
rDoc.Load(FilePath);
DataSet ds = new DataSet();
CrystalReportViewer1.ReportSource = rDoc;
CrystalReportViewer1.Visible = true;
}
protected void Button1_Click(object sender, EventArgs e)
{
MemoryStream oStream= new MemoryStream (); // using System.IO
switch (DropDownList1.SelectedItem.Text )
{
case "Pdf":
oStream = (MemoryStream)rDoc.ExportToStream(CrystalDecisions.Shared.ExportFormatType.PortableDocFormat);
Response.Clear();
Response.Buffer = true;
Response.ContentType = "application/pdf";
Response.AddHeader("Content-Disposition", "attachment;filename=SearchResult.pdf");
Response.BinaryWrite(oStream.ToArray());
Response.End();
break ;
case "Doc":
oStream = (MemoryStream)rDoc.ExportToStream(CrystalDecisions.Shared.ExportFormatType.WordForWindows);
Response.Clear();
Response.Buffer = true;
Response.ContentType = "application/doc";
Response.AddHeader("Content-Disposition", "attachment;filename=SearchResult.doc");
Response.BinaryWrite(oStream.ToArray());
Response.End();
break;
case "Excel":
oStream = (MemoryStream)rDoc.ExportToStream(CrystalDecisions.Shared.ExportFormatType.Excel);
Response.Clear();
Response.Buffer = true;
Response.ContentType = "application/vnd.ms-excel";
Response.AddHeader("Content-Disposition", "attachment;filename=SearchResult.xls");
Response.BinaryWrite(oStream.ToArray());
Response.End();
break;
}
}
}