A schematic diagram for Sony hardware (board MBX-252). Shared as “MBX 252 PDF (PK).pdf” — a .pdf file, 1010 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 @pkbiosbdv. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.