It is recommended to use app.config instead of such config unless there is truly exists demand for such design.
You need to map the config file through
ExeConfigurationFileMap Class[
^]
Try this-
ExeConfigurationFileMap fileMap = new ExeConfigurationFileMap();
fileMap.ExeConfigFilename = @"D:\YourFolder\myown.config";
System.Configuration.Configuration config = ConfigurationManager.OpenMappedExeConfiguration(fileMap, ConfigurationUserLevel.None);
string constring=config.AppSettings.Settings["con"].Value.ToString();
Hope, it helps :)