Download UFT / QTP 12.51. Go here.
2. Click on Download Now link.
3. You will be redirected to below page.
4. You can Sign Up or Sign In (if you already have an account). I created a new account and signed in.
5. On clicking 'Sign In' (above), below screen opens. Click 'Next' in below screen.
6. Click 'Go To MyAccount'.
7. Click on Download.
8. You can download a full installation package or a compressed package.
9. I downloaded the full installation package. It's around 2 GB.