A 34.5 KB PDF for the 2sk2579, indexed with schematics but named only by part number, so it is most likely a compact component datasheet. In JIS semiconductor numbering the 2SK prefix denotes an N-channel field-effect transistor. The small file size suggests condensed content: pinout, package and key electrical limits. That is enough to orient meter probes, judge whether a reading indicates failure and select a replacement part. Match the code printed on the transistor with this number before proceeding.
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.