I have 200 page document filled with references of other authors work e.g John (1996), Smith & Will (2001), Nancy et al. 2006 etc. I wanted to check that whether I have provided the detailed reference for all these citations at the end. so I am looking for a way where I can find the all year numbers i.e. 1999, 2003 etc and replaced them with same number but highlighted (let say in yellow).

So how can I search for any four number digit and return the same number with desired formating.