The package bibtex-utils provides the function bu-jump-to-doc which takes you from a bibtex citation in a document to the pdf of that document. You'll need to bind it to a convenient key. For more details, and some related functions for dealing with Bibtex databases, see the home page for the package linked above.
If you use bibtex keys in different modes (i....
One strategy that is very simple is to define a function, and bind it to a convenient key. Here is one example. You just type C-o on a key, this function finds the key, then uses bibtex-completion to open it.
(defun open-key-at-point ()
(let (start end key)
(setq start (progn (re-...