Hi

Please refer below smaple for excel, And refer below link for PDF.

Export ASP.Net GridView to PDF with Custom Columns Widths using iTextSharp

HTML

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" Font-Names="Arial">
    <Columns>
        <asp:BoundField DataField="ID" ItemStyle-Height="150" HeaderText="ID" />
        <asp:BoundField DataField="Name" ItemStyle-Height="150" HeaderText="Image Name" />
        <asp:TemplateField ItemStyle-Height="150" ItemStyle-Width="170" HeaderText="Image Preview">
            <ItemTemplate>
                <asp:Image ID="Image1" runat="server" ImageUrl='<%# Eval("ID", GetUrl("ImageCSharp.aspx?ImageID={0}"))%>' />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<asp:Button Text="ExportToExcel" runat="server" OnClick="printExcel_Click" />

Namespaces

C#

using System.Configuration;
using System.Data.SqlClient;
using System.Data;
using System.IO;

VB.Net

Imports System.IO
Imports System.Data.SqlClient
Imports System.Data

Code

C#

CS.aspx.cs

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection conn = new SqlConnection(constr))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter("select ID, Name from tblFiles order by ID", conn))
            {
                DataTable dt = new DataTable();
                sda.Fill(dt);
                GridView1.DataSource = dt;
                GridView1.DataBind();
            }
        }
    }
}

protected string GetUrl(string page)
{
    string[] splits = Request.Url.AbsoluteUri.Split('/');
    if (splits.Length >= 2)
    {
        string url = splits[0] + "//";
        for (int i = 2; i < splits.Length - 1; i++)
        {
            url += splits[i];
            url += "/";
        }
        return url + page;
    }
    return page;
}
public override void VerifyRenderingInServerForm(Control control)
{
    /* Verifies that the control is rendered */
}
protected void printExcel_Click(object sender, EventArgs e)
{
    Response.Clear();
    Response.Buffer = true;
    Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls");
    Response.Charset = "";
    Response.ContentType = "application/vnd.ms-excel";
    StringWriter sw = new StringWriter();
    HtmlTextWriter hw = new HtmlTextWriter(sw);
    foreach (TableCell cell in GridView1.HeaderRow.Cells)
    {
        cell.BackColor = GridView1.HeaderStyle.BackColor;
    }
    foreach (GridViewRow row in GridView1.Rows)
    {
        row.BackColor = System.Drawing.Color.White;
        foreach (TableCell cell in row.Cells)
        {
            if (row.RowIndex % 2 == 0)
            {
                cell.BackColor = GridView1.AlternatingRowStyle.BackColor;
                cell.Width = 200;
                cell.Height = 150;
            }
            else
            {
                cell.BackColor = GridView1.RowStyle.BackColor;
                cell.Width = 150;
                cell.Height = 100;
            }
            cell.CssClass = "textmode";
        }
    }
    GridView1.RenderControl(hw);
    string style = @"<style> .textmode { mso-number-format:\@; } </style>";
    Response.Write(style);
    Response.Output.Write(sw.ToString());
    Response.Flush();
    Response.End();
}

ImageCSharp.aspx.cs

protected void Page_Load(object sender, EventArgs e)
{
    if (Request.QueryString["ImageID"] != null)
    {
        string strQuery = "select Name, ContentType, Data from tblFiles where id=@id";
        String strConnString = System.Configuration.ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        SqlCommand cmd = new SqlCommand(strQuery);
        cmd.Parameters.Add("@id", SqlDbType.Int).Value = Convert.ToInt32(Request.QueryString["ImageID"]);
        SqlConnection con = new SqlConnection(strConnString);
        SqlDataAdapter sda = new SqlDataAdapter();
        cmd.CommandType = CommandType.Text;
        DataTable dt = new DataTable();
        cmd.Connection = con;
        try
        {
            con.Open();
            sda.SelectCommand = cmd;
            sda.Fill(dt);
        }
        catch
        {
            dt = null;
        }
        finally
        {
            con.Close();
            sda.Dispose();
            con.Dispose();
        }
        if (dt != null)
        {
            Byte[] bytes = (Byte[])dt.Rows[0]["Data"];
            Response.Buffer = true;
            Response.Charset = "";
            Response.Cache.SetCacheability(HttpCacheability.NoCache);
            Response.ContentType = dt.Rows[0]["ContentType"].ToString();
            Response.AddHeader("content-disposition", "attachment;filename=" + dt.Rows[0]["Name"].ToString());
            Response.BinaryWrite(bytes);
            Response.Flush();
            Response.End();
        }
    }
}
private DataTable GetData(SqlCommand cmd)
{
    DataTable dt = new DataTable();
    String strConnString = System.Configuration.ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
    SqlConnection con = new SqlConnection(strConnString);
    SqlDataAdapter sda = new SqlDataAdapter();
    cmd.CommandType = CommandType.Text;
    cmd.Connection = con;
    try
    {
        con.Open();
        sda.SelectCommand = cmd;
        sda.Fill(dt);
        return dt;
    }
    catch
    {
        return null;
    }
    finally
    {
        con.Close();
        sda.Dispose();
        con.Dispose();
    }
}

VB.Net

VB.aspx.vb

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
        Using conn As SqlConnection = New SqlConnection(constr)
            Using sda As SqlDataAdapter = New SqlDataAdapter("select ID, Name from tblFiles order by ID", conn)
                Dim dt As DataTable = New DataTable()
                sda.Fill(dt)
                GridView1.DataSource = dt
                GridView1.DataBind()
            End Using
        End Using
    End If
End Sub

Protected Function GetUrl(ByVal page As String) As String
    Dim splits As String() = Request.Url.AbsoluteUri.Split("/"c)
    If splits.Length >= 2 Then
        Dim url As String = splits(0) & "//"
        For i As Integer = 2 To splits.Length - 1 - 1
            url += splits(i)
            url += "/"
        Next
        Return url & page
    End If
    Return page
End Function

Public Overrides Sub VerifyRenderingInServerForm(ByVal control As Control)
End Sub
Protected Sub printExcel_Click(ByVal sender As Object, ByVal e As EventArgs)
    Response.Clear()
    Response.Buffer = True
    Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls")
    Response.Charset = ""
    Response.ContentType = "application/vnd.ms-excel"
    Dim sw As StringWriter = New StringWriter()
    Dim hw As HtmlTextWriter = New HtmlTextWriter(sw)
    For Each cell As TableCell In GridView1.HeaderRow.Cells
        cell.BackColor = GridView1.HeaderStyle.BackColor
    Next
    For Each row As GridViewRow In GridView1.Rows
        row.BackColor = System.Drawing.Color.White
        For Each cell As TableCell In row.Cells
            If row.RowIndex Mod 2 = 0 Then
                cell.BackColor = GridView1.AlternatingRowStyle.BackColor
                cell.Width = 200
                cell.Height = 150
            Else
                cell.BackColor = GridView1.RowStyle.BackColor
                cell.Width = 150
                cell.Height = 100
            End If
            cell.CssClass = "textmode"
        Next
    Next

    GridView1.RenderControl(hw)
    Dim style As String = "<style> .textmode { mso-number-format:\@; } </style>"
    Response.Write(style)
    Response.Output.Write(sw.ToString())
    Response.Flush()
    Response.End()
End Sub

ImageVB.aspx.vb

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If Request.QueryString("ImageID") IsNot Nothing Then
        Dim strConnString As String = System.Configuration. _
            ConfigurationManager.ConnectionStrings("constr") _
            .ConnectionString
        Dim strQuery As String = "select Name, ContentType," _
           & " Data from tblFiles where id=@id"
        Dim cmd As SqlCommand = New SqlCommand(strQuery)
        cmd.Parameters.Add("@id", SqlDbType.Int).Value = _
            Convert.ToInt32(Request.QueryString("ImageID"))
        Dim con As New SqlConnection(strConnString)
        Dim sda As New SqlDataAdapter
        cmd.CommandType = CommandType.Text
        cmd.Connection = con
        Dim dt As New DataTable
        Try
            con.Open()
            sda.SelectCommand = cmd
            sda.Fill(dt)
        Catch ex As Exception
            dt = Nothing
        Finally
            con.Close()
            sda.Dispose()
            con.Dispose()
        End Try
        If dt IsNot Nothing Then
            Dim bytes() As Byte = CType(dt.Rows(0)("Data"), Byte())
            Response.Buffer = True
            Response.Charset = ""
            Response.Cache.SetCacheability(HttpCacheability.NoCache)
            Response.ContentType = dt.Rows(0)("ContentType").ToString()
            Response.AddHeader("content-disposition", _
                "attachment;filename=" _
              & dt.Rows(0)("Name").ToString())
            Response.BinaryWrite(bytes)
            Response.Flush()
            Response.End()
        End If
    End If
End Sub

Screenshot