In a C# application I always used an app.config file to save some data for my application to load when needed (e.g Connection String).
Wha
In iOs every App has own sandbox which will be availble for that app only. So If you want that file to be read only access save it to Application Bundle. else save to Application folder.
you Can not access Application folder directly So If you want to save your file to that folder you have to do it programmatically.