If you see a link promising a "Full Version" of the or the latest Magknight for free on a random file-sharing site, be extremely cautious.
to your X-Plane 11 directory: X-Plane 11 > Aircraft > Extra Aircraft . Paste the folder there. boeing 787 x plane 11 full free download
There is a dedicated freeware 787-8 project available on the X-Plane.org forums created by community members. If you see a link promising a "Full