A 1.51 MB zip labelled only with Apple board number 820-3437; the name states no model or revision. Apple uses the 820 prefix for its logic board part numbers, so expect a schematic, a boardview or both inside. Such documents help with tracing signals between chips, checking expected voltages on rails and finding where a short sits. After extracting, open PDFs in any reader and boardview files in OpenBoardView or FlexBV, and compare the board number and revision on the PCB before relying on the data.
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.