Since the introduction of the term hypertext in the early 1960s, the goal has been to link, annotate as well as transclude parts of documents. However, most existing document linking approaches show some shortcomings in terms of the offered link granularity and cannot easily be extended to support new document formats. More recently, we see new document formats such as the Office Open XML (OOXML) standard which facilitate the linking to parts of certain document formats. We present a dynamically extensible open cross-document link service enabling the linking and integration of arbitrary documents and multimedia content. In our link browser, emerging document formats are supported via visual plug-ins or by integrating third-party applications via gateways. The presented concepts and architecture for dynamic extensibility improve the document life cycle in so-called cross-media information spaces and enable future-proof cross-document linking.