Datasheet for the 2SD875 NPN transistor, supplied as a 43 KB PDF; the _E suffix in the name most likely marks an English-language edition, though this is not certain. Under JIS naming, 2SD parts are NPN low-frequency transistors. A technician would use the document to check the pinout, electrical ratings, hFE ranks and package outline when testing a component in circuit or finding an equivalent. Always verify the marking on the device and the board footprint before relying on these figures for a replacement.
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.