Most online casinos do not require you to provide any documents when making withdrawals especially if you have already verified your casino account. You may however be asked to provide verification documents such as Identity card or passport, driving license or bank statement or utility bill as proof of residential address when making a first time withdrawal.
Some online casinos may also require you to provide documentation for making large withdrawals. It is therefore advisable to check out the withdrawal terms and conditions of the specific online casino when making a withdrawal request.