ExeConfigurationFileMap map = new ExeConfigurationFileMap();

            map.ExeConfigFilename = @"C:\App.config"; ;

            Configuration config = ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);

            string connstr = config.ConnectionStrings.ConnectionStrings["connStr"].ConnectionString;

            MessageBox.Show(connstr);

            string key = config.AppSettings.Settings["key"].Value;

            MessageBox.Show(key);