private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        {
            SqlConnection cn = new SqlConnection(@"Data Source=(LocalDB)v11.0;AttachDbFilename=E:Documentsbasededadospap.mdf;Integrated Security=True;Connect Timeout=30");
            try
            {
                cn.Open();
                string query = "select * from fornecedor where nomefornecedor='" + comboBox1 + "'";
                SqlCommand createCommand = new SqlCommand(query, cn);
                SqlDataReader dr = createCommand.ExecuteReader();
                cn.Close();
            }

            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }