A boardview (component placement) file (board 15264-1). Shared as “15264-1.main board.brd” — a .brd file, 136 MB.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @alischematics. Enginerys does not host this file.
How to open a .brd file
The most common boardview extension. Several unrelated formats share it, which is why one viewer opens a .brd and another refuses it.
OpenBoardViewFlexBVBoardViewerAllegro Free Physical Viewer (Allegro .brd only)