A 206 KB PDF named only 2SC5148, filed with schematics but describing a single part. In the Japanese JIS system the 2SC prefix denotes an NPN bipolar transistor, so the file is most likely its datasheet with limit values, characteristic curves and outline. Technicians use it to identify leads, confirm power and voltage ratings, and judge replacements when a transistor stage has failed. Any PDF reader opens it; the name gives no maker or revision, so check the part marking on the board first.
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.