Small ZIP archive of about 109 KB tied to the Apple logic board number 820-01124; the name gives no model, document type or revision, so the contents must be inspected before use. Apple marks its main boards with 820-prefixed part numbers, and that code is the reliable way to match a file to a MacBook board. Given the size, it may hold a boardview, a firmware image or a short document rather than a full schematic. Check the 820 number silkscreened on the PCB matches before relying on anything inside.
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 @notebookschematic. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.