Each bought/borrowed book is associated with an AbobeID.
You can use an AdobeID on up to 6 devices ... that includes any computers running ADE needed for getting the books onto the devices.
So it is technically fairly easy for up to 5 devices to share, though sharing that way may be against the strict ts&cs of a book.
So you'd probably need 3 copies of the book.
Also, if the devices are used by their readers for their own private books as well that makes it even more complex.
Each device can only be associated with one ID.
Thank you for your reply sjpt !
Is there no enterprise version of ADE for my need of sharing document ?
I'm pretty sure there isn't. The restriction is more on the book than on the software used to read it.
The publishers expect to get paid for each person who is going to install and read the book.
There have been quite a few queries from librarians who have similar (not identical) issues,
and I haven't seen an answer suggesting any useful alternatives.
You could try asking Adobe directly, but I'm not too hopeful of a good answer for you. Good luck.