I have a particular document that needs to have a list of all those who have accessed it. It cannot be through Audit Trail as it needs to be accessible by those who do not have access to Audit Trail.

I was thinking I could have a field where the name gets recorded (preferably automatically) when the document is opened, but how do I add the user name to the field? 

Using Workflow would be my first choice, but I can use Forms. I would like to keep user interface to a minimum.

Is there a better option? I am open to ideas.