Component datasheet for the 2SK2661, a 385 KB PDF that is indexed as a schematic. Under JIS naming, the 2SK prefix marks an N-channel field-effect transistor, so look here for device ratings and pin identification rather than board wiring. Typical uses include confirming lead order before desoldering, checking gate threshold and breakdown voltage, and comparing cross-reference candidates. Similar-sounding parts in the same number range can differ, so match the exact printed code before trusting the figures.
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.