The scroll, parchment or leaf (not the whole book) gains protection against being copied. When the spell is cast the forces that bind the object together are now replaced by magic.
The spell can also detect when it is being copied. If someone tries to copy the document, as the words are being copied the words on the original document are being erased. Once the copied word count reaches 10 then the spell is broken and the document denigrates.
If a dispel magic is cast on the document then the spell is removed and the document disintegrates.
Documents protected by this spell will detect as magic (as magic is infused with the document).
Casting this spell on a magic scroll will cause the following effect. The scroll could still be used to cast magic, but if someone tried to copy the scroll into their spell book the scroll would disintegrate before the copy could be completed.
Consequences of casting a spell scroll with the first several words of the spell missin will be left up to the DM.