1. Open Notepad and type “what are you doing” without quotes. 
Note: Don’t press enter after typing.
2. Save it with your desired name and close it.
3. Now open that Notepad document again….surprise!! You can’t see anything you have just typed, instead you see boxes or symbols. 
The reason is notepad in ANSI or UNICODE encoding cannot recognize any text of the form 4-3-3-5. And if you want to see the text again you can do it by accessing the file using command prompt or save the file in UTF-8 encoding.
@Dustin Thanks for your valuable comment, mate. I have edited the post so that the steps are lot easier to follow. By the way the trick works fine. Try it out again