A compact 134 KB PDF titled with the part number 2SK2839 and catalogued as a schematic. Japanese JIS naming uses 2SK for N-channel field-effect transistors, so this is probably a brief datasheet or summary sheet for that device. It helps when identifying pins, reading maximum ratings and judging whether a cross-reference part is suitable. The smaller size may mean fewer pages or graphs than usual. Check the full marking on the component and its package against the drawing before soldering in a substitute.
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.