I searched the "Has this question already been asked?" option and didn't see an answer so I'll ask:

How does one attach a document in a Private Message or Forum Email? I'm reasonably sure I've done it before but can't seem to figure out how to do it today :bonk:

Actually, no. The Private Message and Forum Email functions do not support attachments. I *think* there is a 'hack' for the Private (Personal) Email system to allow attachments but not for the 'Blind' Forum Email system. I haven't installed the Private Message hack (obviously), but I'll take a look at it.

Right now the best way is to trade email addresses in Private Messages and then to use your email client to send things to each other through your regular email accounts.