Besides, if you want to collect multiple payments I assume you have to encrypt that file for each person, right?
Because once somebody pays all of them are decrypted....
No ! File decrypted only one time for the payer ...
You encrypt it one time and spread it over internet, and then many persons can buy it (if someone decrypt it, not all persons that got the archives will be decrypted for him, each one of them must pay for custom decryption)... and by the developer the decryption is different from person to another, good security thinked there.