FileIOReaderHelper.cs

public interface IFileIoReaderHelper
{
     string ReadFromDefaultFile(string fileName);
}
	
public class FileIOReaderHelper : IFileIoReaderHelper
{
     //Read the content from Json file 
     public string ReadFromDefaultFile(string fileName)
     {
         if (string.IsNullOrWhiteSpace(fileName))
         {
             throw new ArgumentNullException(nameof(fileName));
         }

         Uri appUri = new Uri(fileName);

         IStorageFile anjFile = StorageFile.GetFileFromApplicationUriAsync(appUri).AsTask().ConfigureAwait(false).GetAwaiter().GetResult();

         string txtFile = FileIO.ReadTextAsync(anjFile).AsTask().ConfigureAwait(false).GetAwaiter().GetResult();

         return txtFile;
     }
}