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.)
This exact scenario happened with me in a prior job. Invoices, payments, everything could (and sometimes was) sent through WhatsApp. It was absolutely shocking to see people do this.
I witnessed a cop attempting to manipulate some files I provided to him on a thumb drive. It was a slow laborious process of dragging files one at a time from the Windows image viewer to shared folder. I would have liked to just do a Ctrl-A, Ctrl-C, Ctrl-V, but that was way above his level of thinking and he didn't seem like the type who wanted an education. So I just sat there through the long, painful process--and then at the end he completely screwed up the report. Idiot.