RAR archive of 13.8 MB labelled for the LG G4 H815 smartphone. The name does not list the contents, so it may hold schematics, a service manual, board layouts or other repair material for that model; extract it with WinRAR, 7-Zip or a similar tool to see what is inside. Such packs are typically used to trace power rails, find test points and check component placement during board-level repair. Verify the model code on the handset is H815, as other G4 variants use different boards.
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 @schematic_mobiles. 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.