Large applications that have evolved over the years, are often well-functioning and reliable, but have severe problems regarding flexibility and reuse. It is hard to migrate such systems to a more flexible architecture or to new technologies. The document archive/retrieval system discussed in this paper is an example system, that has these problems. We will present a reengineering case study based to component technology based on an architectural pattern language. The patterns aim at the introduction of flexibility into blackbox component architectures in a piecemeal way.