The 2SD1409A file is a 212 KB PDF listed among schematics; a name made only of a part number strongly suggests a datasheet, and the A suffix denotes a variant of the 2SD1409. JIS nomenclature uses 2SD for NPN transistors in low-frequency service. Use it to identify the leads, read maximum collector voltage, current and dissipation, and compare equivalents before soldering. It opens in any PDF reader, and the device case usually shows D1409A without the 2S prefix.
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.