To be fair, what other simple way is there to send a document to a contact through an e2ee channel? Mail + PGP/GPG? Wormhole?? openssl???
Sending it via WhatsApp (which also has desktop clients, btw) strikes me as a perfectly reasonable solution. (Which is somewhat of an indictment of the current state of cryptographic software, but that's a different topic.)
Whatsapp "claims" to be e2e, but nobody knows for sure since its sources are closed.
Still more secure than non encrypted email yet a lot of people still use email to send fairly sensitive data.