A boardview (component placement) file. Shared as “5k-gal_top_mb-11-Eng-20190521-5asc-Basic.pcb” — a .pcb file, 1.36 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 @ShareMan_Electronic_Files. Enginerys does not host this file.
How to open a .pcb file
In repair archives a .pcb is typically an XZZ (XinZhiZao) boardview — popular for phones and recent laptops.
XZZ PCB viewerOpenBoardView (recent builds)FlexBV