The biggest thing is when you save your documents, you need to change the format to .doc or .xls or other people will not be able to open your documents.
I'm not sure if it's there in the later versions, but there isn't support for .docx or .xlsx in the free office suites I've used.
As for buying it, it was less than £20 last time I looked on CD Keys for standard Office 2019. 2019 was the last, non-cloud version.
You mean the most current. MS have committed to more "Offline" versions. They realise that not everyone can use Microsoft 365 for a host of reasons.
.doc and .xls and so on are proprietary formats, which is why so many non MS products make a real hash of reading anything but the simplist documents. .docx and .xlsx and so on are openly publish formats owned and controlled by MS, so no reason not to support them in your open source tools, but again most implementations make a mess of it.
£20 for an illegal hooky key sounds extortionate BTW. If you want to be hooky, there are millions of resources out there for how to do it for free. But obviously we do not allow that sort of discussion here.
I didn't realise they had more offline versions available, I've just avoided it
I admit it's been a few months, but neither of the free tools I tried then supported docx/xlsx.
With regards CD Keys, whilst you can never be certain of the origins of the key, they do guarantee them. So at least you can prove you've tried. I posted this as it's likely more legal than other sources which we obviously don't mention.