ZIP archive of 3.47 MB named after the ASUS P8B75-M CSM desktop motherboard, an Intel B75 chipset board. The name does not state the contents, but files of this size for desktop boards usually hold a BIOS image or service material. When it contains a BIOS dump, compare its size with the SPI flash chip on the board, keep a backup of the original chip read with a programmer, and check the board model silkscreen before writing anything, because similar ASUS variants use different images.
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 @biositechyangiyer. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.