From what I remember, the EU wanted to standardize an open document format, and had their eye set on OO ODF, as the most mature of those at the time. Microsoft put out their OXML format, gave out free patent grants, lobbied hard, and managed to get it into ISO.
If you want some nightmares though, open an office XML file in a text editor some day.
They came with Office 2007. For Office 2003, there was a plugin that allowed to open the XML files, in a limited way.
I wrote that and on a whim thought, "I'll make this a pip package," severely underestimating that task. The tool works but I never finished that packaging. The working source should be on github if you're interested.
It is really quite distinct from the memory dump of pre-xml doc/excel files.
I woulda cobbled something together to suck the text out of them.
The real problem was using word as our documentation format, but at Microsoft in the early oughts there really weren't many alternatives.
The cobble-together part, to be successful, would pull the text out reliably. And the format is readily documented, and Open/Libre office processes it as well. The code to do the extract might be ugly, but so long as it reliably produced the text in a CI/CD environment, that would be OK.