The keyfile feature is only implemented for backward compatibility with AxCrypt 1.7 – so you can open files encrypted then with a keyfile.
We’ve decided not to implemented this feature, because it has caused some problems with very small benefits. You can choose to use a very good password instead – why not use a string similar to what’s in the keyfile for example? Exactly the same level of security.
The problem with keyfiles are that they need to be stored somewhere, and it’s very hard to ensure this is done properly.
We may in the future support various hardware tokens instead.