How do you set a document to be only visible to the assigned user(s)

My client want to be able to upload documents in admin and assign them to specific users so when that user logs into the frontend they, and only they, have access to the relevant document?

I have assigned documents to a specific user in the admin and found that it is still visible to any logged in user.

Hi Crispin,
When you modify document at Back-end side, there is field: Owner ID(s), here you can select specific user as owner of document. And only he(she) can see document at front-end
Thanks
Dam