A boardview (component placement) file. Shared as “Hz4tv-d3.cst” — a .cst file, 17.1 KB.
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 .cst file
Text boardview from the Castw tool chain, typical for older ThinkPad boards.
OpenBoardViewBoardViewer