The name of this 176 KB PDF consists only of 2SC3790, a JIS-style part number in which 2SC denotes an NPN transistor. Although catalogued as a schematic, it is most plausibly a component datasheet, and nothing else about the device is given in the name. Technicians typically use these to map leads, check breakdown voltage and collector current, and find a cross-reference when a power or driver stage has failed. Match the marking and package on the physical part before treating the document as authoritative.
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.