Issue in save and retreive file in postgres

Greetings,

I am a software programmer and  working on a .net web application(ASP.NET 4.0, c# ).
I am new to postgres and for my current project I am using postgres as database.


In this need functionality to upload a pdf file  to database and then retrieve it again from database.
I have taken bytea column in my table to store binary file data. I am taking byte array to convert the data.

When I try to retrieve this pdf file from database ,its not working.
Please see the below code and suggest me some solution.

Here is my code:
3. ##########   Database table ############

CREATE TABLE testimage
(
  id integer,
  img bytea
)

2. ##########   function to save file in database 
protected int UploadDocumentsPostgres()
    {
        int result = 0;
        if (fuDocuments.HasFile)
        {
            fuDocuments.SaveAs(Server.MapPath("Temp/") + fuDocuments.FileName);

            using (FileStream pgFileStream = new FileStream(Server.MapPath("Temp/" + fuDocuments.FileName), FileMode.Open, FileAccess.Read))
            {
                using (BinaryReader pgReader = new BinaryReader(new BufferedStream(pgFileStream)))
                {
                    byte[] pgByteA = pgReader.ReadBytes(Convert.ToInt32(pgFileStream.Length));
                   
                    NpgsqlConnection cn = new NpgsqlConnection("server=195.100.1.100;port=5433;database=DTMS;user id=postgres;password=admin@123");
                   
                    NpgsqlCommand cmd = new NpgsqlCommand();
                    cmd.Connection = cn;
                    cn.Open();
                    string sql = "insert into testimage values(@id,@data)";

                    cmd.Parameters.Add("@id", NpgsqlTypes.NpgsqlDbType.Integer, 1).Value = 1;
                    cmd.Parameters.Add("@data", NpgsqlTypes.NpgsqlDbType.Bytea, pgByteA.Length).Value = pgByteA;
                   
                    cmd.CommandText = sql;
                    cmd.ExecuteNonQuery();
                    cn.Close();

                }
            }
        }
        return result;
    }


3.    ###################   Retrieve file from database and save in temp folder ########################
DataTable dt = new DataTable();
        NpgsqlConnection cn = new NpgsqlConnection("server=195.100.1.100;port=5433;database=DTMS;user id=postgres;password=admin@123");
        NpgsqlDataAdapter sda = new NpgsqlDataAdapter("select * from testimage", cn);
        sda.Fill(dt);


        if (dt.Rows.Count > 0)
        {
            byte[] doc = (byte[])(dt.Rows[0]["img"]);
            FileStream fs = new System.IO.FileStream(Server.MapPath("Temp/") + "temp.PDF", FileMode.Create, FileAccess.Write);
            BinaryWriter bw = new BinaryWriter(new BufferedStream(fs));

            bw.Write(doc, 0, doc.Length);
            bw.Flush();
            bw.Close();
            fs.Close();
        }
--
Thanks & Regards
Vishwas Dwivedi
Contact No: +91-9460968854