Track documents that have been read

HI

I have a request to track the documents in a doc library.  The documents in the library have to be read by users of the portal.  Each time the user logs in, they will be provided with a list of the documents that they are required to read.  As soon as a user has read / opened a document, the item is flagged as read by the that user.

I cannot find any events that fire on document read/open.  I was thinking of added an ECB menu and forcing the user to selected when they have read the document.  Then have a field against the document to store all the users that have read the marked the document as read,

Can anyone think of a better way of doing this.

Thanks in advance