Filed under schematics, this 80.8 KB PDF is titled with the part number 2SC2857. The JIS 2SC prefix designates an NPN bipolar transistor, so the content is most likely a short component datasheet; no other details appear in the name. Such a document gives the pin arrangement, absolute maximum ratings and key electrical parameters needed when testing or substituting a transistor. Measure the removed part out of circuit, and confirm the marking and package on the board component before using this data for a replacement.
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.