Protecting a document in an email

Hi,

There is a scenario where customer would like to send docs to his clients (external users) with view only permission as an attachment in emails.

He would like to restrict them from editing & taking print out (if possible)

If we implement IRM its necessary that clients should also have IRM (Correct me, if I am wrong)

or Can we set permission on Office docs & attach them in emails & send (Is it possible, if yes what versions it supports)

I tried setting up "Mark as final" in word 2013 but it allows user to disable it.