That's how the DOC format in the 90s and early 00s worked. I was under the impression that the early formats for Word on DOS, Windows and Macintosh were all different and represented in-memory structures written directly to disk. Unfortunately, I can't find a citation, so I may be mistaken.
There was certainly some format that Word and Excel used before compound files, since COM Structured Storage only appeared in 90s, and the first version of Office to use it was (IIRC) Office 97. That older format may well be some kind of a memory dump. But I don't think there are many Office files still floating around these days, and most third party software that works with them seems to assume that it's 97 or later.
