I think you can try accessing options under the LocalFolder under your appData. For example there are methods like CreateFile, GetFileAsync, OpenFileAsync etc.
await ApplicationData.Current.LocalFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);
Try using GetFileAsync and based whether you get a valid o/p or hit exceptions you can move forward with what you want to do.
Do check
http://msdn.microsoft.com/en-us/library/windows/apps/windows.storage.applicationdata.aspx[
^] for more information on Application Data