All the existing/old document formats that don't migrate well (ignoring physical transfer) have a common issue, they're
binary formats which makes them quite a lot harder to write decent decoders for (on future software) and they're typically very brittle (one bad bit and usually the decoder will run off the rails crashing into the bit-bin).
Plain-text formats with tags/formatting on the other hand can be migrated with a lot of ease, at worst you can still strip out the raw text or write your own decoded based on a few assumptions. Things like LaTeX, RTF, HTML/XML, TXT etc can stand the test of time because the format is inherently readable (Even Postscript is to a fairly reasonable degree, depends on how your brain is wired
).
We've (computer scientists and programmers) know this for a long time but during the earlier computing eras with limited space we started cramming everything into bit-fields with some incredibly masterful (but insane) formats, there was also the market-security-via-obscurity aspect too (hence formats like ms-doc).
I'm glad to see that the latest developments of document have come back to being easy to parse, fault tolerant formats.
... video and audio files on the other hand are just scary ... but at least they're well documented
