sending documents dont always work,
you dont have the guests original e-mail, and i found out severla times Airbnb is filtering the e-mails
you send.
meaning sometimes the guest does not receive the information you want them to receive.
house manual is not sufficient in my opinion,
since we have electronic locks on our properties and every guest is receiving a specific code
(same goes for the alarm code)
also you want them to be able to print it out at home and bring it with them.
specially international guests who have no data roaming in other countries will be happy with such an option.
the safest way is to store your document (either in DOC or PDF format)
in the " cloud" (dropbox, one drive or any other third party)
and send your guest a share to the file, they can download it
you can send the link over with the regular message system from Airbnb (which everyone uses) so they can even download the file on their smart phone
simply delete the file after your guest is departed and there is no mess of files you need to store
hope this helps others
gerhard