own ipad that previous owner doesn't remember password

As FoxFifth has already mentioned, if the previous owner does not remember the password or won't help you after presenting them with the article that was provided, no one here, including Apple, will be able to help you with this. As far as Apple is concerned, this iPad is potentially lost or stolen.

With Activation Lock, it's impossible to get into the iPad without the e-mail and password. If you have bought this from someone, you should to try to return it. Or else, it's a paperweight.

There is no known way to bypass activation lock without the assistance of the previous owner. The previous owner can get help with the password: If you forgot your Apple ID password - Apple Support