How to rename a file with appended numbers if another file already exists with the same name in asp.net c# web form application?

Hello Experts.

I'm using Visual Studio 2012 and SqlServer 2012.  

I am using a fileupload control to upload files to the web server.  Whenever a file with the same name already exists, I would like to have that filename changed by adding a number to the end.  For example, contract.docx, contract(1).docx, contract(2).docx, etc...  I have seen this question answered many time on EE, as well as Stackoverflow and other sites.  Unfotrtunately, I haven't been able to successfully modify my code to help me do that.  

The code I have right now is straight-forward, and just overwrites original files with the new file if the filenames are the same.  Here is what I have right now:

protected void btn_frm_new_doc_save_close_Click(object sender, EventArgs e)
        {
            if (fu_doc_upld.HasFile)
            {
                fu_doc_upld.PostedFile.SaveAs(Server.MapPath("~/Data/") + fu_doc_upld.FileName);
            }
            hdn_filename_txt.Value = (Server.MapPath("~/Data/") + fu_doc_upld.FileName.ToString());
            hdn_doc_uplod_dt_txt.Value = DateTime.Now.ToString();

            SqlConnection idrf_cnxn = new SqlConnection("Data Source=MYSRVR;Initial Catalog=idrf;Integrated Security=True");
            {
                SqlCommand new_doc_cmd = new SqlCommand("Insert Into tbl_doc(doc_title, doc_type_list, doc_org_list, doc_dept_list, doc_desc, prior_contract_cd, legal_comp_contract_id, doc_upld_dt, doc_path, vendor_id_fk) Values(LTRIM(RTRIM(@doc_title)), LTRIM(RTRIM(@doc_type_list)), LTRIM(RTRIM(@doc_org_list)), LTRIM(RTRIM(@doc_dept_list)), LTRIM(RTRIM(@doc_desc)), LTRIM(RTRIM(@prior_contract_cd)), LTRIM(RTRIM(@legal_comp_contract_id)), LTRIM(RTRIM(@doc_upld_dt)), LTRIM(RTRIM(@doc_path)), LTRIM(RTRIM(@vendor_id_fk)))", idrf_cnxn);
                new_doc_cmd.Parameters.AddWithValue("@doc_title", doc_title_txt.Text);
                new_doc_cmd.Parameters.AddWithValue("@doc_type_list", doc_type_ddl.Text);
                new_doc_cmd.Parameters.AddWithValue("@doc_org_list", doc_org_ddl.Text);
                new_doc_cmd.Parameters.AddWithValue("@doc_dept_list", doc_dept_ddl.Text);
                new_doc_cmd.Parameters.AddWithValue("@doc_desc", doc_desc_txt.Text);
                new_doc_cmd.Parameters.AddWithValue("@prior_contract_cd", prior_contract_cd_txt.Text);
                new_doc_cmd.Parameters.AddWithValue("@legal_comp_contract_id", lgl_comp_cont_id_txt.Text);
                new_doc_cmd.Parameters.AddWithValue("@doc_upld_dt", hdn_doc_uplod_dt_txt.Value);
                new_doc_cmd.Parameters.AddWithValue("@doc_path", hdn_filename_txt.Value);
                new_doc_cmd.Parameters.AddWithValue("@vendor_id_fk", hdn_vendor_id_txt.Value);

                idrf_cnxn.Open();
                new_doc_cmd.ExecuteNonQuery();
                idrf_cnxn.Close();

                if (IsPostBack)
                {
                    Response.Redirect("~/Default.aspx");
                }
            }
        }

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How can I modify this to not overwrite existing files with the same names, but instead rename the files as stated above?

Please let me know if you need additional information.

Your help is greatly appreciated.

Thanks,
J