How to cache file loaded inside the iFrame

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ASP.NET

I have an aspx program where i want to load a file inside the iFrame. And it is loading fine. But after loading when one wants to add feedback then after clicking feedback button the file Unloads automatically, and have to load again.

the code for loading model and feedback is:

protected void Feedback_Click(object sender, EventArgs e)
{
    try
    {
        WebGLApp1.Feedback.CreateFeedbackTable();
    
    }
    catch(Exception)
    {

    }
    string Uname = Session["username"].ToString();
    string Fname = Session["filename"].ToString();
    string Object="Object1";
    string Fback=TextBox1.Text;
    WebGLApp1.Feedback.InsertFeedBack(Uname, Fname, Object, Fback);
    TextBox1.Text = null;
    BindGridviewDataFeedback(Fname);
   
}

protected void lnkLoadModel_Click(object sender, EventArgs e)
{

    
    LinkButton lnkbtn = sender as LinkButton;
    GridViewRow gvrow = lnkbtn.NamingContainer as GridViewRow;

    int fileid = -1;
    for (int cnt = 0; cnt < gvDetails.Rows.Count; cnt++)
    {
        if (gvrow.RowIndex == gvDetails.Rows[cnt].RowIndex)
        {
            fileid = cnt;
            break;
        }
    }

    //int nFieldCount = gvDetails.Rows[fileid].Cells.Count;
    string Name = gvDetails.Rows[fileid].Cells[0].Text.Trim();
    //Name = gvDetails.Rows[fileid].Cells[1].Text;
    Session["filename"] = Name;
    using (SqlConnection con = new SqlConnection(strCon))
    {
        using (SqlCommand cmd = new SqlCommand())
        {
            cmd.CommandText = "Use iVizDatabase;select FileName, FileType, FileData from FileManager where Number=@ID ";
            cmd.Parameters.AddWithValue("@Id", fileid+1);
            cmd.Connection = con;
            con.Open();
            SqlDataReader dr = cmd.ExecuteReader();

            if (dr.Read())
            {
                Response.ContentType = dr["FileType"].ToString();
                Response.AddHeader("Content-Disposition", "attachment;filename=\"" + Name + "\"");
                Response.BinaryWrite((byte[])dr["FileData"]);
                Response.End();
            }
        }
    }
}