Small ZIP archive of 121 KB labelled S300CA, version 2.0, with no brand or board number in its name. At that size it most likely holds a compact document such as a schematic PDF or a boardview, though the contents have to be confirmed after extraction. S300CA reads like a model or project code rather than a motherboard part number, so compare the code and the 2.0 revision printed on the board before working from it. Typical use is checking power sequencing, tracing signals and finding components near a fault.
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 @ITHINKHS. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.