the error storing and retriving pdf file from and to database

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C#

VB

I was told to reference default1 to default2 once upload button has been clicked,
it returns invalid operation exception was unhandled by user code
Fill: SelectCommand.Connection property has not been initialized.

Default1

using System;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
using System.IO;


namespace Defult
{
    public partial class _Default : System.Web.UI.Page
    {
        //SqlConnection sqlcon = new SqlConnection("PDF_Files");
        SqlCommand sqlcmd = new SqlCommand();
        //SqlDataAdapter da = new SqlDataAdapter();
        DataTable dt = new DataTable();
        protected void Page_Load(object sender, EventArgs e)
        {

            if (!Page.IsPostBack)
            {
                LoadGrid();
            }
            Label1.Text = "";

        }

        void LoadGrid()
    {
        //SqlConnection sqlcon = new SqlConnection("PDF_Files");
        SqlCommand sqlcmd = new SqlCommand("select * from Files");
       SqlDataAdapter da = new SqlDataAdapter(sqlcmd);
        da.Fill(dt);
        if (dt.Rows.Count > 0)
        {
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
        //sqlcon.Close();
    }

        protected void Button1_Click(object sender, EventArgs e)
        {
            //PDF Upload Code to SQL SERVER database table
            if (FileUpload1.HasFile)
            {
                Stream fs = default(Stream);
                fs = FileUpload1.PostedFile.InputStream;
                BinaryReader br1 = new BinaryReader(fs);
                byte[] pdfbytes = br1.ReadBytes(FileUpload1.PostedFile.ContentLength);
                
                SqlCommand sqlcmd = new SqlCommand("insert into Files(pdfname,pdfcontent) values (@pdfname,@pdfcontent)");
                sqlcmd.Parameters.Add("@pdfname", FileUpload1.FileName);
                sqlcmd.Parameters.Add("@pdfcontent", pdfbytes);
                sqlcmd.ExecuteNonQuery();
                //sqlcon.Close();
                Label1.Text = "Successfully pdf upload to SQL Server database.";
                LoadGrid();
            }

        }


    }
}

Default2

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;

namespace Defult
{
    public partial class Default2 : System.Web.UI.Page
    {
        SqlConnection sqlcon = new SqlConnection(ConfigurationManager.ConnectionStrings["PDF_Files"].ConnectionString);
        SqlCommand sqlcmd = new SqlCommand();
        SqlDataAdapter da = new SqlDataAdapter();
        DataTable dt = new DataTable();
        string qstr;
        byte[] b = null;

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                qstr = Request.QueryString["ID"];
                //Read PDF file from DATABASE table pdf field
                SqlCommand sqlcmd = new SqlCommand("Select pdfcontent from pdfupload where ID='@ID" + qstr + "'", sqlcon); 
                //use condition to retrieve particulatr PDF
                sqlcon.Open();
                da = new SqlDataAdapter(sqlcmd);
                da.Fill(dt);
                if (dt.Rows.Count > 0)
                {
                    b = ((byte[])dt.Rows[0][0]);
                    //Collect Bytes from database and write in Webpage
                    Response.ContentType = "application/pdf";
                    Response.BinaryWrite(b);
                }
            }
        }
    }
}