I don't know much about adult adoption or adoption in general, just that it is common practice in case a close relative has for example a serious mental illness so you can make decisions for the person in question.
The path to citizenship is only possible for minors or those who pretend to be. And yes, you're right, you don't have to give up anything for that except maybe - speculating here - it's connected to some inheritance law that you have to leave the adopted child a minimum amount of your property.