How to export a datagrid values in PDF

protected void Page_Load(object sender, EventArgs e) 
{ 
if (!Page.IsPostBack) 
{ 
String strCon = System.Configuration.ConfigurationManager 
.ConnectionStrings["EmpDBConnectionSring"].ConnectionString; 
SqlConnection con = new SqlConnection(strCon); 
con.Open(); 

string strSQL = "SELECT * FROM Emptab"; 
SqlConnection con = new SqlConnection(strCon); 
SqlDataAdapter da = new SqlDataAdapter(strSQL, con); 
DataSet ds = new DataSet(); 
da.Fill(ds, "test"); 

GvEmp.DataSource = ds.Tables[0]; 
GvEmp.DataBind(); 
} 
} 
protected void Button1_Click(object sender, EventArgs e) 
{ 

Response.Clear(); 
Response.AddHeader("content-disposition", "attachment; filename=EmployeeDetails.pdf"); 
Response.Charset = ""; 
System.IO.StringWriter stringWrite = new System.IO.StringWriter(); 
System.Web.UI.HtmlTextWriter htmlWrite = 
new HtmlTextWriter(stringWrite); 
GvEmp.RenderControl(htmlWrite); 
Response.Write(stringWrite.ToString()); 
Response.End(); 

} 

Imports iTextSharp.text.pdf
Imports iTextSharp.text
Imports System.IO
Imports System.Data
Imports System.Data.SqlClient
Partial Class _Default
    Inherits System.Web.UI.Page
    Dim ds As New DataSet

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not Page.IsPostBack Then
            '  ShowGridview()
        End If
    End Sub
     
    Sub ShowGridview()
        'bind the database values to Gridveiw using dataset control
        Dim con As SqlClient.SqlConnection
        Dim da As SqlDataAdapter

        Dim str As String
        str = "USER=UserID;PASSWORD=PASSWORD;SERVER=SERVER-Name;DATABASE=DATABASE-Name"
        con = New SqlConnection(str)
        da = New SqlDataAdapter("select FieldName1,FieldName2 from Table_Name", con)
        da.Fill(ds, "Employee")
        ViewState("DataSetValue") = ds
        grvGrid.DataSource = ds
        grvGrid.DataBind()
        con.Close()

    End Sub
    Private Sub ConvertGridviewToPdfDocument(ByVal dstHeader2 As DataSet)
        Dim doc As Document = New Document
        PdfWriter.GetInstance(doc, New FileStream(Request.PhysicalApplicationPath + "\3.pdf", FileMode.Create))
        doc.Open()
        Dim table As New PdfPTable(dstHeader2.Tables(0).Columns.Count)
        Dim widths As Integer() = {25, 25}
        table.WidthPercentage = "100"
        For i As Integer = 0 To dstHeader2.Tables(0).Columns.Count - 1
            Dim ColumnHeader As New Paragraph(dstHeader2.Tables(0).Columns(i).ColumnName.ToString(), FontFactory.GetFont("verdana", 11))
            ColumnHeader.Font.SetStyle(Font.BOLD)
            Dim cell As New PdfPCell(New Phrase(ColumnHeader))
            cell.HorizontalAlignment = Element.ALIGN_CENTER
            table.AddCell(cell)
        Next

        For k As Integer = 0 To dstHeader2.Tables(0).Rows.Count - 1
            For j As Integer = 0 To dstHeader2.Tables(0).Columns.Count - 1
                Dim ColumnValue As New Paragraph(dstHeader2.Tables(0).Rows(k)(j).ToString(), FontFactory.GetFont("verdana", 10))
                table.AddCell(ColumnValue)
            Next
        Next
        table.SetWidths(widths)
        doc.Add(table)
        doc.Add(New Paragraph(vbLf))
        doc.Close()
        Response.Redirect("~/3.pdf")
    End Sub
    
    Protected Sub btnConvertGridviewToPDF_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnConvertGridviewToPDF.Click
        'ConvertGridviewToPdfDocument(ViewState("DataSetValue"))
        Dim str As String = ""
        Dim doc As Document = New Document
        PdfWriter.GetInstance(doc, New FileStream(FileUpload1.PostedFile.FileName, FileMode.Create))
        'string strFileNameWithPath = FileUpload1.PostedFile.FileName;
        doc.Open()
        doc.Close()

    End Sub
End Class