A .lxf file is a three-dimensional model or scene created by LEGO® Digital Designer (LDD), another great product developed by the LEGO Company.
It can be loaded and refined by LDD.
In a nutshell, the LDD allows you to build and modify LEGO brick models. Detailed information on the LEGO Digital Designer can be found on Wikipedia.
Minecraft® is trademarked and copyrighted by Mojang and its licensors. LEGO® is a trademark of the LEGO Group of Companies. All rights reserved. Xplicator, Craftplicator and Brickplicator are not official Minecraft® or LEGO products and are not associated, approved or endorsed by these companies or their licensors in any way.