Named for the 2SC2555, this 186 KB PDF is filed under schematics but is most likely the component's datasheet. Under the JIS system the 2SC prefix identifies an NPN transistor, and the prefix is usually dropped from the body marking, leaving something like C2555. Technicians open documents like this in any PDF reader to confirm the lead order and limiting values. That matters when choosing a substitute, because equivalents from other makers can swap the base, collector and emitter positions.
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.