This week's book giveaway is in the Reactive Progamming forum. We're giving away four copies of Reactive Streams in Java: Concurrency with RxJava, Reactor, and Akka Streams and have Adam Davis on-line! See this thread for details.
Your best bet is probably to use OpenOffice in server mode. It can open and save all kinds of formats -including HTML and DOC- and has a Java API to drive it. The JODConverter library makes that process much easier.