Catalogued as a schematic, this 89.4 KB PDF bears the part number 2SC4133, a JIS designation for an NPN bipolar transistor, so its content is most likely the device datasheet. Expect the component itself to be marked C4133. A technician reads such a document for pinout, mechanical package data, breakdown voltages, collector current and gain classes when diagnosing or replacing the part. The name gives no manufacturer or revision, so check the marking and case style on the board to make sure the specifications match.
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.