PDF of 77.6 KB named 2SD1620 and filed with schematics; the name carries nothing beyond the part number, which points to a component datasheet. A 2SD part in the JIS system is an NPN bipolar transistor for low-frequency service. The usual value of such a sheet lies in the pinout drawing, ratings table and characteristic curves, used to test the transistor out of circuit and to choose an equivalent with equal or higher limits. Look for D1620 on the package, the common short form.
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.