RAR archive of 6.96 MB labelled BH5899 V1.2; the name gives only a board code and version, with no brand, model or content type. Unpack it with 7-Zip or WinRAR to find out whether it contains a schematic, boardview or firmware image. Before using the material for tracing rails, locating components or reflashing, check that the BH5899 marking and V1.2 revision are printed on your own board, since revisions often differ in parts and layout.
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 @ShareMan_Electronic_Files. 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)