This document contains both the libwpd API specification and the normal libwpd documentation.
The external libwpd API is provided by the WPDocument class. This class, combined with the librevenge::RVNGTextInterface class, are the only two classes that will be of interest for the application programmer using libwpd.
If you are interrested in the structure of libwpd itself, this whole document would be a good starting point for exploring the interals of libwpd. Mind that this document is a work-in-progress, and will most likely not cover libwpd for the full 100%.