PayPal Setup Question

Since the CS-Cart 2 user manual is entirely too vague on most things, I have a question about PayPal setup for 2.0.12.

In 1.3.5, I used a PayPal certificate titled cert_key_pem.txt. In v. 2, it defaults to a cert named paypal_cert.txt.

So, should I use the cert_key_pem.txt certificate from the old site or the paypal_cert.txt certificate from the new site?