The 2SK1461 in the file name is a JIS-style code for an N-channel FET, so this 120 KB PDF, though listed as a schematic, is expected to be its datasheet. It should provide absolute maximum ratings, electrical characteristics and the pin and package details a technician needs before testing or replacing the part. Such data helps decide whether an alternative MOSFET can stand in safely. Confirm the marking on the transistor matches exactly, since this series contains many near-identical numbers.
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 @cyberlanelectonik. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.