An archive of repair files. Shared as “TP.MS358.PB818_4G_512M_REF35USB Boot.rar” — a .rar file, 320 MB.
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 @hashmielecom. 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)