I see, you are talking about remote contracts, here you need to upload a scan (or photo) of the actual document + (not all but many will) have a video call where you must show yourself holding the same document you already uploaded.
AFAIK the "other party" has no way to check that the ID is not fake, nor a way to verify that the document number corresponds to you, so - in theory - you could print a fake id with a random number and it would work the same.
Little by little they are introducing a form of digital ID (SPID, provided by authorized third parties) that while not yet ubuquitous is starting to get traction (it is already needed to deal with most government offices remotely) also in private sectors.
AFAIK the "other party" has no way to check that the ID is not fake, nor a way to verify that the document number corresponds to you, so - in theory - you could print a fake id with a random number and it would work the same.
Little by little they are introducing a form of digital ID (SPID, provided by authorized third parties) that while not yet ubuquitous is starting to get traction (it is already needed to deal with most government offices remotely) also in private sectors.