There is only one file type that uses the .LDR extension:
LDraw Model File
File created by LDraw, a suite of CAD tools used to build digital 3D LEGO models; contains the dimensions of LEGO bricks and their placements within a 3D coordinate system; used for saving LEGO designs.
The term "LDraw" can actually refer to different things, including the original DOS LDraw program, the LDraw parts library, the LDraw tool suite, or the LDraw standard file format. It most commonly refers to the file format or the LDraw tool suite.
The LDraw tool suite includes MLCAD (Mike's LEGO Computer Aided Design) for constructing LDR files, LDview for viewing LDR files, and other tools for converting LDR files to the .POV format.
NOTE: LDR files are saved in a plain text format.
Updated: February 11, 2019