An archive in RAR format, roughly 959 KB, for the Xiaomi Mi 4S phone. The name lists only the model, with no indication of document type, PCB number or revision, so inspect the contents after extraction. Material like this is usually a schematic set, used to trace supply rails from the power management chip, check USB and charging lines, and identify capacitors or filters on a faulty net. Compare the board version printed on the PCB with the drawings to avoid working from a different hardware revision.
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.