I don’t understand how you expect the verification of a physical book to work. You’d have to scan/OCR the entire book to verify the signature.
Alternatively you could do a hash/signature per page to make verification of a single page easier.
Many public keys chain-linked with one master key - are just for example
Have a look at Merkle trees.
UPNP is a security nightmare, better to never enable it at all or if you must only for those networks where you need it.