RAR archive of 326 KB labelled H81M-CT, which points to a desktop motherboard built around the Intel H81 chipset in micro-ATX form. The name gives no brand, revision or content type, so the archive could hold a BIOS image, a schematic or other service material; open it and inspect the files before use. If it contains a firmware dump, compare its size with the SPI flash chip on the board, save a backup of the original chip contents with a programmer first, and confirm the model and revision silk-screened on the PCB match.
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 @boardview. 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.