It appears that the functionality to create a temporary file was omitted from Windows 8 / 10
If anyone knows this to not be the case then please add a comment to that effect.
Consequently, I decided to create a little helper method:
public static async Task<StorageFile> CreateTempFile( StorageFolder folder, string extension) { string fileName = string.Empty; while (true) { // Get a random filename fileName = string.Format("{0}.{1}", Guid.NewGuid().ToString(), extension); // Check if it already exists IReadOnlyList<StorageFile> fileList = await folder.GetFilesAsync(); // If it does then loop until we have a unique one if (!fileList.Any(f => f.DisplayName == fileName)) break; } var newFile = await folder.CreateFileAsync(fileName); return newFile; }