PDF documentation for the 2SD1090 transistor, 198 KB, catalogued under schematics though the name indicates a component datasheet. Per the JIS standard, a 2SD part is an NPN bipolar transistor intended for low-frequency circuits. The larger file size suggests characteristic curves and outline drawings beyond a basic ratings table. Consult the pinout and maximum voltage and current before replacing the device, and check the gain class if the circuit depends on matched 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.