Archive for the Apple iMac A1419, EMC 3070, logic board 820-01134-A, where A is the board revision. Apple 820- numbers identify the logic board itself, so matching this number on your board matters more than the model name. At 4.23 MB the package likely holds a schematic or boardview for tracing power rails, locating components and checking shorts. Open schematics in a PDF reader and boardview files in tools such as OpenBoardView or FlexBV, after confirming the 820 number on the PCB.
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 @SCHEMATICWORLD. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.