Internal Hyperlinks and licences

Hi

We us ES4 produce PDFs and would like to have internal hyperlinks - eg: click on a heading in the contents page and it takes you to the relevant page.

We've been told by a contractor that we can do this but would need to upgrade our licence to do it.  We currently have the "Output" licence.  Does anyone know what licence we'd need to do this - or preferably, if there's a way to do the internal hyperlinks on our current licence?

Thanks

Dan