Word History. Bruce Damer's Personal Histories of the Desktop User Interface, at the DigiBarn Computer Museum, talks about the origins of Microsoft Word and its funky file format:
Charles Simonyi and most of the BravoX team left Xerox for Microsoft as a group, around about 1982 or 1983. The first version of MS Word, which appeared maybe a year later, was essentially just a port of BravoX to MS-DOS. If you read the BravoX manual, you can see that it already has MS Word features such as Styles. MS Word also shows its ancestry in its native file format. Bravo and BravoX stored out files by essentially just dumping the memory heap. This made saving and loading documents very fast, but it also meant that a) the file format was not at all easy to decode, and b) some strange stuff, such as previously deleted text, is stored out along with live text. These idiosyncrasies of the file format are still present in the current version of MS Word.