Read And Write Text in text file in asp.net using C sharp

try

        {

            StringBuilder obj1 = new StringBuilder();

            string sCon = string.Empty;

            string scon1 = string.Empty;

            using (StreamReader sr = new StreamReader("file path" + "file name"))

            {

                sCon = sr.ReadToEnd();

            }

            obj1.Append(sCon.Substring(0, sCon.IndexOf("#spoint") + 11) + Environment.NewLine);

            int startpoint = sCon.IndexOf("#spoint") + 11;

            int endpoint = sCon.IndexOf("#epoint");

            string Test = sCon.Substring(startpoint, endpoint - startpoint);

            if (Test.IndexOf("line Name ") > -1)

            {

                obj1.Append(Test);

            }

            obj1.Append("New string append" + Environment.NewLine);

            obj1.Append(sCon.Substring(sCon.IndexOf("#epoint")) + Environment.NewLine);

            scon2 = obj1.ToString();

           

            FileStream fsPattern = File.OpenWrite("file path" + "file name");

            Encoding encPattern = Encoding.ASCII;

            byte[] restPattern = encPattern.GetBytes(obj1.ToString());

            fsPattern.Write(restPattern, 0, objPattern.Length);

            fsPattern.Flush();

            fsPattern.Close();

            fsPattern.Dispose();

        }

        catch (Exception ex)

        {

        }