If you sent them by web form, you'll get an email response saying that they've been forwarded to the relevant office once they've processed the request.question to those who have sent extra documents voluntarily. is there any kind of indication or update you get that they have been received and updated?
my gckey has said "The additional documents you provided have been uploaded." since last year when i sent their requested documents such as PCC and Sched A. i have recently sent some docs voluntarily and wanted to check if they have received/updated my file
If you sent by mail, I don't know if you'll get any feedback.
Note, however, that my experience with this is only relevant to the Mississauga office. I don't know if different Visa Offices have different procedures.