The 2SD2049 is documented in this 131 KB PDF, catalogued as a schematic. In the JIS system, 2SD stands for an NPN bipolar transistor aimed at low-frequency or power applications. Contents should include ratings, hFE ranking, characteristic curves and an outline drawing. Use it to map the pins before replacing the part and to compare voltage, current and dissipation figures with possible substitutes. Verify that the marking on the component, often D2049, matches this document.
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.