Hello Jack C,
Already Svante answered the same forums link(https://www.axcrypt.net/forums/topic/keyfile/). Please read the same.
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.