PDF datasheet of about 56 KB for the 2SD661 transistor, with an _E suffix that probably indicates an English edition. As a JIS 2SD type it is an NPN transistor aimed at low-frequency applications. The document should provide the pin configuration, absolute maximum ratings, gain grouping and mechanical drawings needed to verify a component in circuit or select a substitute with equal or better voltage and current limits. Check the device marking and case on the PCB against the outline before ordering parts.
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.