Few copies of these handbooks exist, likely because such circumstances rarely happen. It seems that Armonia Justin Beyondormason (who has a vast amount of knowledge on the rules of the Death Note and Shinigami Laws) possesses some, if not all of them.
It is unknown if all handbooks look alike, but the one Sidoh obtains from Armonia Justin is a long piece of parchment (it appears to be papyrus). There is much writing on it, but it is unknown if all the writing is actually words or just decoration. There are pictures included which detail the rules.
The full content of the handbooks are unknown, but they include a list of "cases in which a Shinigami that has brought the Death Note into the human world is allowed to return to the Shinigami realm."
"I. When the Shinigami has seen the end of the first owner of the Death Note brought into the human world and has written that human’s name into his or her own Death Note.
II. When the Death Note is destroyed and cannot be used by humans anymore.
III. If nobody claims ownership of the Death Note, it is unnecessary to possess anyone.
IV. If, for any reason, the Shinigami possessing the Death Note is replaced by another Shinigami.
V. When a Shinigami loses track of the Death Note that he or she possesses, or cannot identify where the owner is, and therefore needs to find such information using the observation holes in the Shinigami realm.
VI. Even in cases II, III, and IV, Shinigami are obliged to confirm the death of the first owner and write down that human’s name in his or her Death Note even when he or she is in the Shinigami realm."
- "When the Shinigami does not exist [the Shinigami must] touch the notebook and attach [itself] to the human who has the notebook. [The Shinigami] must stick around until that human dies, and then get the notebook back before some other human picks it up, or get that human to give the notebook to [the Shinigami]."
- "A Shinigami who has dropped their notebook in the human world and is presently without a notebook [is] allowed to be in the human world as an exemption, but [is] not allowed to talk about any other notebook beside their own. Any Shinigami who breaks this rule will die after receiving second-degree agony."