RAR archive of 8.13 MB named after the GT-I9300, Samsung's model code for the Galaxy S III, though the name does not list what files are inside. Extract it with WinRAR or 7-Zip to see whether it holds schematics, layouts or service documents. Material for this phone is typically used to trace power rails, locate components and test points, and diagnose charging or no-boot faults. Check the contents and model code on the board against your device before relying on them.
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 @uzb4422. 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.
7-ZipWinRARThe Unarchiver (macOS)