Nope. Making a complete "backup" of a book doesn't fall under fair use. PG simply making a digital copy to put in the PG vault (for release in 20xx) would be a violation of copyright. Stupid but that is the reality of our utterly broken copyright system.
The only exemption for making a backup is computer software. Not books, not movies, not ebooks, not any other form of copyrighted material.
One can make a partial copy (for example photocopying pages from a reference manual) which technically is a violation of copyright but falls under fair use protection but fair use doesn't extend to complete copy except in the case of computer software.
What makes it even worse is that DMCA will in the future make even the creation of archiving tools a crime. Say in 80 years there is an interest for PG but for movies. Someone making software to break encryption on movies would have a legitimate use however DMCA doesn't provide any carve-out for legitimate use and thus the software would be prohibited and creators and distributors in violation of the law.
We have in the span of less than a century turned a wonderful idea; providing LIMITED protection to content creators to encourage such content into something that now only holds back innovation. Pathetic. In 2034 Mickey Mouse will go into public domain. In 2030 Disney will lobby (and if the past 3 times are any indication win) to extend copyrights to 120 years after death of author. Then in another 50 years they will do it again and again and again and again.
Essentially the pool of public domain works will never grow because companies will never allow their "property" to become public domain. Even marginal works have some value. Companies can simply buy up copyrights for negligible amounts hoping that some future work will be derived from it and sue for compensation. The copyright equivalent of patent trolls.