The name offers nothing beyond the 2SD2500 part number, and the 250 KB PDF is almost certainly that transistor's datasheet. Japanese JIS coding uses 2SD for NPN bipolar transistors suited to low-frequency circuits. Repair technicians open it in a PDF reader to find lead order, power dissipation, hFE grouping and voltage limits, useful when tracing a failed stage or testing junctions with a meter. Compare the package drawing with the physical part and confirm the D2500 marking before replacing it.
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.