The 2SD2634 transistor is described in this 30.7 KB PDF, classified as a schematic though the name points to a datasheet. JIS designations starting with 2SD indicate NPN transistors intended for low-frequency circuits. A technician reads such a document for pin assignment, maximum ratings, hFE classification and package outline, all needed when testing a failed part or selecting an equivalent from another maker. Any PDF viewer will open it. Match the body marking on the component before ordering, since short codes vary.
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.