RAR archive of 833 KB named G5_EF10MIX; the name does not identify the brand, device or content type, and the EF10MIX token has no certain meaning. It could be a BIOS or firmware package or a document for a G5 model, so extract it and check the files before acting. If it contains a flash image, read and save the original chip with a programmer first, compare the image size against the chip capacity and confirm the board number matches. If it is a schematic or boardview, verify the board revision printed 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 @cyberlanelectonik. 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.