NanaR wrote: A friend asked me recently if authors must pay a fee to submit a work to receive the Nihil Obstat and/or the Imprimatur.
I honestly didn't know, although it seems to me that there might be some sort of administrative fee for something like this.
There is no canonical fee, but an administrative fee certainly seems reasonable. No one is required to submit any publication for approval; the Imprimateur is protection for the reader that nothing contained in the publication is contrary to Catholic teaching, but anyone who wishes may publish anything they want without approval.
(Some religious orders do require that their members submit anything to be published for approval, but that is a requirement of the order, not the Church.)