A 429 KB PDF titled 2SK2789 and stored among schematics, most likely the datasheet for that part. In the JIS designation scheme 2SK refers to N-channel FETs, so the sheet should include absolute maximum ratings, electrical characteristics and an outline drawing. Repair technicians use it to identify pins before in-circuit testing, to understand normal behaviour, and to vet substitute MOSFETs. The name offers no maker or package detail, so check the physical marking on the PCB part first.
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.