[p_l]

SQLite would not be a good choice.

DOC file format, combined with OLE containers, was designed at least partly to deal with common practice of keeping documents on floppies, and to make saving documents as speedy as possible.

This meant a combination of pseudo filesystem (OLE containers can be summarised as a variation of FAT filesystem) and blittable data structures. This way when you saved an updated version of the document, Word would only extend the file with new changes, minimizing amount of I/O necessary.

Another aspect to this was that DOC was not supposed to be interchange file format - that's a role that was supposed to belong to RTF. Which was much easier to parse and had formal, published specification instead of memory dumps of internal data structures. However it took a more resources to update such file, so RTF and DOC were kept in sync when it came to capabilities all the way to Office 2003 - everything you could do in DOC, you could do in RTF, and vice-versa.

Of course, practice quickly went in different direction and most people only think of RTF as the simpler sibling of DOC, because WordPad on Windows used it.