Hi  Waghmare,
I have modified your code please check.
HTML
<div>
    <asp:GridView ID="gridInformation" runat="server" AutoGenerateColumns="false" Font-Names="Arial"
        OnRowDataBound="gridInformation_RowDataBound">
        <Columns>
            <asp:BoundField DataField="EmployeeId" HeaderText="EmployeeID" />
            <asp:BoundField DataField="EmployeeName" HeaderText="EmployeeName" />
            <asp:TemplateField HeaderText="Pics" ItemStyle-Height="160" ItemStyle-Width="180">
                <ItemTemplate>
                    <asp:Image ID="empimage" runat="server" ImageUrl='<%# Eval("FilePath", GetUrl("{0}")) %>' />
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
    <br />
    <asp:Button ID="btnExportWord" CommandArgument="Word" runat="server" Text="Export-Word"
        OnClick="Export_Grid" />
    <asp:Button ID="btnExportExcel" CommandArgument="Excel" runat="server" Text="Export-Excel"
        OnClick="Export_Grid" />
    <asp:Button ID="btnExportPDF" CommandArgument="PDF" runat="server" Text="Export-PDF"
        OnClick="Export_Grid" />
</div>
C#
protected void Page_Load(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.Add("EmployeeId", typeof(int));
    dt.Columns.Add("EmployeeName", typeof(string));
    dt.Columns.Add("FilePath", typeof(string));
    dt.Rows.Add(1, "Peter", "Files/00000001.jpg");
    dt.Rows.Add(2, "John", "Files/00000002.jpg");
    dt.Rows.Add(18, "Thomas Hardy", "Files/00000018.jpg");
    dt.Rows.Add(101, "Christina Berglund", "Files/00000101.jpg");
    dt.Rows.Add(1001, "Yang Wang", "Files/00001001.jpg");
    gridInformation.DataSource = dt;
    gridInformation.DataBind();
}
protected void Export_Grid(object sender, EventArgs e)
{
    Button btn = (Button)sender;
    switch (btn.CommandArgument)
    {
        case "Word":
            Word_Export();
            break;
        case "Excel":
            Excel_Export();
            break;
        case "PDF":
            PDF_Export();
            break;
    }
}
public override void VerifyRenderingInServerForm(Control control)
{
    /* Verifies that the control is rendered */
}
private void Word_Export()
{
    try
    {
        Response.Clear();
        Response.Buffer = true;
        Response.AddHeader("content-disposition", "attachment;filename=EmployeeInfo.doc");
        Response.Charset = "";
        Response.ContentType = "application/vnd.ms-word ";
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        gridInformation.AllowPaging = false;
        gridInformation.DataBind();
        gridInformation.RenderControl(hw);
        Response.Output.Write(sw.ToString());
        Response.Flush();
        Response.End();
    }
    catch (Exception)
    {
    }
}
private void Excel_Export()
{
    try
    {
        Response.Clear();
        Response.Buffer = true;
        Response.AddHeader("content-disposition",
            "attachment;filename=EmployeeInfo.xls");
        Response.Charset = "";
        Response.ContentType = "application/vnd.ms-excel";
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        gridInformation.AllowPaging = false;
        gridInformation.DataBind();
        for (int i = 0; i < gridInformation.Rows.Count; i++)
        {
            GridViewRow row = gridInformation.Rows[i];
            //Apply text style to each Row
            row.Attributes.Add("class", "textmode");
        }
        gridInformation.RenderControl(hw);
        //style to format numbers to string
        string style = @"<style> .textmode { mso-number-format:\@; } </style>";
        Response.Write(style);
        Response.Output.Write(sw.ToString());
        Response.Flush();
        Response.End();
    }
    catch (Exception)
    {
    }
}
private void PDF_Export()
{
    try
    {
        Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition", "attachment;filename=EmployeeInfo.pdf");
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        gridInformation.AllowPaging = false;
        gridInformation.DataBind();
        gridInformation.RenderControl(hw);
        StringReader sr = new StringReader(sw.ToString());
        Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 0f);
        HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
        PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
        pdfDoc.Open();
        htmlparser.Parse(sr);
        pdfDoc.Close();
        Response.Write(pdfDoc);
        Response.End();
    }
    catch (Exception)
    {
    }
}
protected string GetUrl(string imagepath)
{
    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 + imagepath;
    }
    return imagepath;
}
protected void gridInformation_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
    }
}
Screenshot 

I hope works for you.