The 2SD1212 is the subject of this 120 KB PDF, filed as a schematic. Based on the Japanese JIS numbering, 2SD marks an NPN transistor meant for low-frequency circuits, so the file is most probably a component datasheet. Look for maximum voltage and current, power dissipation, gain bands and a lead diagram. It supports bench testing, correct orientation when refitting and selection of an equivalent, where package style, pinout and ratings should all match or exceed the original part.
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.