[NTG-context] jump to document

I want to jump from the generated pdf to an external document. For example to something like file:///Volumes/MYDISK/users/me/Documents/thisone.jpg. Especially when writing a document that refers to many external documents this makes referencing back to sources a lot easier. I tried to find how to do it from the reference manual but did not succees. Help will be appreciated. Hans van der Meer