A 186 KB PDF identified by the part number 2SC2873 and classed as a schematic. Under the JIS standard the 2SC prefix means an NPN bipolar transistor, so this is most likely a datasheet for that single component; no maker is named. It is useful for confirming base, collector and emitter positions, maximum ratings and switching or frequency characteristics. Use the figures to pick a cross-reference part if the original is unobtainable, and check the board marking and footprint so the replacement fits correctly.
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.