Whatever book you find important you should have a physical copy of. Books that teach you vital skills, as well as the Bible, should be kept safe somewhere. You cannot rely on only electronic copies, for a few reasons. The electronic copy can be altered, and if no one questions it (or can question it) then the original message in the books will be lost. Even if corrupt powers do not attack the electronic copies, technology can be neutralized by EM pulses from bombs or even massive solar flares.
I am not against technology, but the flaw of it is that we have come to rely on it too much. You can see it with a cashier, most the time the register helps them make change. When they are forced into a situation where they aren’t given the change total by the computer, they either have to take a moment to get into the mindset to do mental math, or they simply can’t make change with their mind anymore unassisted. The ability is lost. Whatever skill is not used because we use technology is weakened or lost.
When the time comes, we will need physical books with knowledge to teach us again what we have lost through atrophy. With books that can survive catastrophe not all is lost, if the worst happens.