Is it possible to block or lock a stolen iPad?

Yes. Follow the steps in the support document you posted from, and mark it as lost.

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

Mark as Lost

When you mark your device as

lost, you remotely lock it with a passcode, keeping your information

secure. This also disables Apple Pay on the missing device. And you can

display a custom message with your contact information on the missing

device. 

Mark your device as lost

You can set it up to be erased, and it will do so once it connects to the internet and receives the command.

As long as you have a passcode it should be fine even if it is a weak one. Attempting wrong passwords will lock the device for increasingly longer periods of time each time. Eventually becoming impossible to enter any passwords.