Untl comparatively recently, the "competition" between WordPerfect and Word
was viewed more like a "cold war" from Microsoft's side (and perhaps to a
lesser extent from WP's side), and they refused to support the format in
any way (WP would read, but not write, Word docs). After WordPerfect sold
itself to Novell, Word surged ahead (because Novell completely bungled
marketing and support-and-enhancement), and Microsoft graciously allowed
former WordPerfect users to convert their documents to Word format.
WordPerfect saw a resurgence when Novell sold it to Corel, and now both
programs will read and write both (all three, really, since MS has both doc
and docx now) formats.
During the "cold war" period, WordPerfect was the word processor of choice
for legal (and government) documents, as it did a better job of supporting
some of the peculiar requirements of the legal profession (e.g., numbering
the lines of a document). Word, however, was generally seen as somewhat
easier to use, and was dominant in most other contexts.