Only the part number 2SK2221 names this small 55 KB PDF, which is catalogued as a schematic but most likely serves as a component datasheet. The 2SK prefix denotes an N-channel field-effect transistor in Japanese JIS/EIAJ notation, and the file name gives no further detail. A technician uses such a sheet for pin identification, maximum ratings and basic characteristics when testing or replacing the device. It also helps when hunting for a cross-reference that fits the same footprint.
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.