No, nothing is further from the truth. In Agile you plan and document all the time, but you keep it lean. You do it quickly and efficiently. You don’t write 50 page documents that nobody is going to read. If you write something you keep it short and simple. You perform Planning in your Sprint Planning sessions prior to starting every sprint and you document all the time by writing down your user stories. You also document your retrospectives and before starting your project you also perform your due diligence (business plan, resourcing, etc. like you would on any project).