Protecting documents on the portal?

Question

Document flow

Hello dear forum users. I have a question for you. A friend of mine recently approached me with the following request. Her small but proud firm is engaged in training. She develops many materials herself and gradually accumulates something like manuals. Life does not stand still and some workers leave and others come in their place. Of course, new teachers need to be given access to developments so that they can both prepare and show them on projectors. But right there it is not difficult to copy these materials to a USB flash drive and take everything home with you. She had a reasonable question as to whether it is possible to somehow limit these rights for certain users. Of course, if it were only about protecting files on a dedicated machine or on several machines, this would not cause difficulties.
And so TK:
We have three types of documents vord.docx, excel.xlsx, and powerpoint.ppt
The total volume is about 5 gigabytes.
What I would like to have:
Read-only access for certain users (teachers for hire) to these documents both at work and at home.
The ability to copy, delete, edit, print these documents only by the director of the company (well, or by several other trusted people).
Reasonable cost for this solution.
We are well aware that it is not possible to protect these documents from print screen and other analog methods in such conditions.
What was done:
A rush of news and archives stumbled upon a seemingly chic solution
Nextcloud 11 gives us the ability to deploy online storage with access settings, and ONLYOFFICE allows us to edit this whole thing in the browser. Everything would be great, but as soon as we get a document to read in ONLYOFFICE, the functionality of this editor allows us to save this document to disk and then do all sorts of outrages with it. Those. the protection function works only with a document that is on the portal, but nothing prevents this document from being saved, and the right mouse button works so that you can stupidly copy everything to the clipboard.
Hence the question dear forum users. Is there any solution to such a problem or is it worth fundamentally changing the policy for distributing files and just shutting down and setting up policies on computers, there are about 5 of them, but in the future opening branches that will not be controlled? In general, you ask for some kind of portal on which there is an online reader of the above documents and the possibility of distributing rights to these documents or folders with documents. Maybe someone else has experienced something similar and has something to share. Thank you all for your attention.

Answer 1

As an example, a ban on downloading, gives Google Docs
There is some kind of support for the formats that you indicated. Perhaps what is needed.

Answer 2

Nothing will save you from copy-pastes ...
Then let them work with printed paper copies.
Well, and, probably, you need to somehow secure yourself legally by consulting a lawyer.