RAR archive for the Z97I-PLUS, a mini-ITX style desktop motherboard model on the Z97 chipset, going by the name. Neither the document type nor the board revision is stated, so open the 371 KB package to see whether it carries a boardview, a schematic or other repair data. Small archives like this usually hold layout or diagram files, which help with tracing VRM rails, checking for shorts and locating test pads. Match the revision printed on the PCB against the files before trusting component positions.
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 @boardview. 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.