don't give them any documents they will abuse it. and will most definitely sell your information to multiple high paying buyers out there to also abuse it.
their platform is also broken and it is already leaking information out:
https://cointelegraph.com/news/bittrex-leaks-user-passports-in-support-emails-says-russian-telegram-channel

not to mention in the end they will close your account, disable withdrawals and rob you blind.