File name 2sk198 is a JIS semiconductor number, so this 31.8 KB PDF, though catalogued as a schematic, is best treated as a brief component datasheet. Devices prefixed 2SK are N-channel field-effect transistors. A technician uses such a document to identify the gate, drain and source pins and to check maximum voltage and current before fitting a replacement. Given the small size, expect only core specifications, and double-check package type and any classification letter on the original part against the sheet.
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.