The 34.0 KB PDF named 2SK3557 is indexed as a schematic, but its name is a JIS component number, so it is almost certainly a datasheet. The 2SK prefix denotes an N-channel field-effect transistor. Technicians use such documents to confirm gate, drain and source positions, package outline and voltage and current ratings when a FET tests shorted. Before substituting, ensure the replacement matches the package and pinout and meets or exceeds the original limits, and check the marking on the board part.
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.