How do i make my program work for 5 times and then Expire

[Lord Orwell]

OK take an easy situation, assuming you may/maynot have used some sort of encryption.
How do you stop a person from doing this thing:

1. I install your appliacation.
2. Copy your zxs.txt to some other location on my computer (say desktop).
3. Run your application 4/5 times or maybe until it expires.
4. Replace your zxs.txt with the original copy (saved on desktop).
5. Run your application again.
6. Repeat this for ever

Pradeep

there are also a bunch of programs out there that reset your computer date to the same date to launch a program and then set it back.