However, it was definitely written to ensure existing doc files could be fully supported, so a lot of the format is “bit 7: if enabled, use Word for Mac 5.0 layout engine.” So… Documented, yes. Usable, no.
PDF, as mentioned, is very similar. The format is available, but no one really wants to implement ALL of it.
docx is OOXML, Open Office XML.
However, it was definitely written to ensure existing doc files could be fully supported, so a lot of the format is “bit 7: if enabled, use Word for Mac 5.0 layout engine.” So… Documented, yes. Usable, no.
PDF, as mentioned, is very similar. The format is available, but no one really wants to implement ALL of it.