Part number 2SD2459 names this 41.2 KB PDF, followed by an unexplained E tag; it is catalogued as a schematic. The 2SD prefix follows the Japanese JIS convention for NPN bipolar transistors, so the contents are probably ratings, characteristic curves and package outline for that part. No device or board is stated. Technicians rely on such sheets to identify collector, base and emitter before testing, and to choose an equivalent. Small transistors are often marked D2459 only, so compare carefully.
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.