Fun fact: on the receiving end they usually have complex systems in place to scan and process those documents back into digital format. And the people working with it pay good money to OCR those scanned documents to make the whole system usable.

This is sometimes referred to as the 'five monkeys with a ladder' paradigm [0] (not to be confused with the '5 monkey experiment'). It basically comes down to: we must use paper format, because we have always done it that way, though nobody knows why we still do it.

Having worked on a paperless accounting startup, I though that paper was still used for legal reasons. It turns out that (for most countries) this is mostly a misunderstanding. Digital documents are just as valid (if not higher level of assurance) as its paper counterparts. Many businesses still insist on the 'signature with a blue ink pen' thing, but again that is due to the 5 monkeys with a ladder problem.

[0] https://skeptics.stackexchange.com/questions/6828/was-the-ex...