if (DocUpload.PostedFile != null || (!String.IsNullOrEmpty(DocUpload.PostedFile.FileName)) || DocUpload.PostedFile.InputStream != null)
                {
                    byte[] imageBytes = new byte[DocUpload.PostedFile.InputStream.Length + 1];
                    DocUpload.PostedFile.InputStream.Read(imageBytes, 0, imageBytes.Length);
 
                    string DocFileName = DocUpload.PostedFile.FileName.ToString();
                    string DocContenttype = DocUpload.PostedFile.ContentType;
                    int DocLength =   DocUpload.PostedFile.ContentLength;
 
                    // Convert the binary input into Base64 UUEncoded output.
           string base64String;
                    base64String = System.Convert.ToBase64String(imageBytes, 0, imageBytes.Length);
 
                    InsertCommand.Parameters.Add(new SqlParameter("@MyDoc", SqlDbType.NText));
                    InsertCommand.Parameters["@MyDoc"].Value = base64String.ToString();
                }

  protected void Button1_Click(object sender, EventArgs e)
    {
        string strQuery = "select Doc_Name,Doc_ContentType,My_DocData from tbl_tablename where ID=@ID'";
        SqlCommand cmd = new SqlCommand(strQuery);
        cmd.Parameters.Add("@ID", SqlDbType.BigInt).Value = 11;
        DataTable dt = GetData(cmd);
        if (dt != null)
        {
            download(dt);
        }  
    }
 private DataTable GetData(SqlCommand cmd)
    {
        DataTable dt = new DataTable();
        String strConnString = System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlConnection con = new SqlConnection(strConnString);
        SqlDataAdapter sda = new SqlDataAdapter();
        cmd.CommandType = CommandType.Text;
        cmd.Connection = con;    
        con.Open();
        sda.SelectCommand = cmd;
        sda.Fill(dt);
        return dt;
    }
 private void download(DataTable dt)
    {
        byte[] bytes = ConvertStringToByteArray(dt.Rows[0]["My_DocData"].ToString());
 
       Response.Clear();
       Response.Charset = "utf-8";
       Response.AddHeader("Accept-Header", bytes.Length.ToString());     
       Response.ContentType = dt.Rows[0]["Doc_ContentType"].ToString(); 
       Response.ContentEncoding = System.Text.Encoding.UTF8;
       Response.AddHeader("Accept-Ranges", "bytes");
       Response.Buffer = true;
       Response.AddHeader("Expires", "0");
       Response.AddHeader("Cache-Control", "must-revalidate, post-check=0, pre-check=0");
       Response.AddHeader("Pragma", "public");
       Response.AddHeader("content-Transfer-Encoding", "binary");   
       Response.AddHeader("content-disposition", "attachment;filename="+ dt.Rows[0]["Doc_Name"].ToString() ; 
       Response.BinaryWrite(bytes);
       Response.Flush();
       Response.End();
    } 
 public byte[] ConvertStringToByteArray(string input)
    {
        System.Text.ASCIIEncoding enc = new System.Text.ASCIIEncoding();
        return enc.GetBytes(input);
    }