Covering the 2SD1246, this 85.2 KB PDF is filed among schematics but its name is simply a JIS transistor number. The 2SD series designates NPN transistors meant for low-frequency use. Sheets of this type give breakdown voltages, collector current, power rating, hFE ranking and the case outline with lead order. It is useful for confirming a shorted or open junction with a meter and for picking a cross-reference part, keeping the original package and pin sequence in mind.
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.