Wen Yan didn't go out; Feng Yao sent someone with a supposedly high-precision, high-resolution scanner to scan the book that Wen Yan had in his possession.
The benefit of books lies in this: replication can be done at a relatively low cost.
The costly part is how to teach people, how to get the knowledge into their minds.
Wen Yan received the photocopied document and then sent a copy to Fourth Great-uncle Master to have a look.
Feng Yao took the photocopied document and reported it, asking experts in the relevant industry to evaluate it.
To be experts in the relevant industry at least, one should be able to discern authenticity and level.
Subsequent evaluations would determine within what range it would be suitable to disseminate after reprinting.
Whether it can be reprinted is actually no mystery; many risky professional books have mature procedures for publication and control of circulation.
