Filed as a schematic, the 124 KB PDF titled 2SC4555 names a discrete transistor, so its content is probably the datasheet. JIS numbering uses the 2SC prefix for NPN bipolar transistors aimed at high-frequency circuits; nothing else is encoded in the name. Technicians reference such documents to confirm pin assignments, breakdown voltages, collector current and dissipation, and hFE grades. Before replacing a failed part, compare package style and marking code on the PCB with the document.
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.