The 2SC5144 is the only detail this 206 KB PDF name carries; despite the schematic label it is presumably the device datasheet for that transistor. The 2SC prefix follows the JIS system and identifies an NPN bipolar part. Datasheets of this kind list absolute maximum ratings, electrical characteristics, typical curves and the mechanical outline, which are what you need to judge whether a replacement is safe in a power or switching stage. Match the exact suffix and package of the original component before substituting anything.
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.