you can use itextsharp for that
protected void btnExportPdf_Click(object sender, EventArgs e)
{
Response.ContentType = "application/pdf";
Response.AddHeader("content-disposition", "attachment;filename=BusinessUnit.pdf");
Response.Cache.SetCacheability(System.Web.HttpCacheability.NoCache);
StringWriter sw = new StringWriter();
HtmlTextWriter hw = new HtmlTextWriter(sw);
GridView grd = new GridView();
grd.DataSource = yourdatatable.DefaultView//get data from DB in Datatable
grd.DataBind();
grd.RenderControl(hw);
StringReader sr = new StringReader(sw.ToString());
Document pdfDoc = new Document(PageSize.A2, 8f, 8f, 8f, 8f);
HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
pdfDoc.Open();
htmlparser.Parse(sr);
pdfDoc.Close();
Response.Write(pdfDoc);
Response.End();
}