Does someone know how to make a standalone pdf file unreadable after some time/date?

The solution I'm looking for must be reliable (not easily bypassed) and universal/specific to the file so not depending to any software (the final user should be able to view the document in any pdf reader during the authorized period).

NB:

• the whole file is meant to be shared externally as a standalone file on other systems I don't know about. So it cannot be a solution related to the initial file system (like some user specific permissions) or to a specific online platform like Google Drive, Dropbox...,
• the file is already protected by a user password in order to be read. One possible hint if possible could be to associate a kind of expiration date to the password itself but I don't know any such solution...

Actually I'm not even sure the solution I'm looking for with all these requirements exists.
According to my searches, I've only found the following tracks:

• incorporate some javascript within the pdf: easily bypassed. In the simplest use case, the user only needs to read the pdf in a protected view/environment which deactivates javascript. Sometimes opening the file in a browser makes the job as well. User can also change his system date backwards.
• use some proprietary solutions:
  • user needs to use a specific solution to read the secured pdf because expiration is dealt with inside the software only. That's out of the question for me.
  • Adobe LiveCycle/Experience Manager Forms associated to a policy server: I think it is based on DRM but the issue here is the Adobe price tag (I read somewhere it could be around 6000$) + I'm not even sure it's software-independent for the final user (I bet the user needs an Adobe product to open the restricted document and connect to a specific server in order to read the content).

Thanks in advance for any suggestion if you have some

I don't think this can be done; I've never heard of a way. It's stupid in any case; During the readable period, I can convert it to ps, html, txt, or a host of other formats, extract the images, print it, or even edit it, all with common utilities on my hd. I can display and photograph it, scan it, or use OCR. Any of those circumvent your protection. I am also capable of remembering it, if it interests me in the least. It sounds like you or your boss more likely has had a brain fart, and needs to be enlightened that his Machiavellian scheme is a non starter.

^ You're right in that any solution my boss and I have found so far are bypassable (not always so easily though). As I said in my OP I'm not sure the solution we are looking after exists!
However, the company I work for just wants to make it harder for anyone to copy the pdf content. That's why there are already a lot of limitations applied to the pdf file associated with an owner password (the one that allows permission modifications). So all your solutions about conversion to ps/html/txt... don't work out-of-the-box actually. However, of course, one can always read the content and scan/photograph/rewrite it eventually or force the security if (s)he is a little bit smarter

You're right. It's not out there. Why not tell your boss there's nothing 100%, except not to write the pdf in the first place. DRM has several clever ways around it. Only controlling access will help. It's good to remember that Sci-hub exists and functions because of usernames/passwords it has collected from various institutions which give it access to restricted content. Of course, as it keeps it's copy, it doesn't have to access them anew each time. He should think about this quote.

I think we'll drop the idea

[OFF]
I didn't know about Sci-hub. What catches my attention is how Sci-hub "collected" these credentials in the first place? Is it by theft (like phishing) or by consent/collaboration?
If the former is true, then it's just really amazing that hacked institutions haven't changed their password so far...or that means there is a continuous hacking process somewhere...
[/OFF]

Personally, I have no usernames/passwords of any institution. I believe there may have been a data dump at some point. But most scientists are principled people, and many were upset at the obvious bias developing in science towards people who could pay. I suspect there were many informal arrangements (American scientists giving user/passwords to counterparts in poorer countries). This is just a website routing around the restriction. For years, sci-hub has collected copies of what they passed through, so now they have in the region of 70% of the restricted papers anyhow.

There's alas unpaywall browser add on, and a scientist can set up a profile on researchgate.net and google scholar to make his information available there.

Not possible.

What you want to do is an example of "Information Rights Management". Just like DRM before it, IRM is entirely reliant on the software enforcing the restrictions set by the file's writer against the possible wishes of the reader opening the file. That means steps have to be taken to impede other software from opening the file, in an attempt to force the reader into only using the official software (invariably proprietary) that enforces the IRM restrictions.