It's a relatively common policy in media stores, I think, despite what the terms on the receipt say.

You don't usually get to return stuff like CDs, books or whatever unless they are faulty/damaged, precisely because they are easily copied, or used and returned.

That's the same for stores in the UK, too, so Qatar isn't any different in that respect.

It's my understanding of English consumer law, for example, that you have no 'right' of return in any event; if you happen to change your mind, it's only possible at the discretion of the store as an act of goodwill. The only 'right' to return goods in English consumer law exists if they are faulty.

You are no worse off being in Qatar than you would be in the UK. In comparative terms, you aren't being treated disrespectfully or being denied any rights you would otherwise have in the UK. (I obviously can't comment on the Qatari legal system and whether or not you have any rights in Qatari law that are being denied to you.)

And tbh, it's hardly their fault that you bought a duplicate of a book you already possessed!