The 2SC3987 document is an 83.4 KB PDF whose name contains only the part number, so expect a transistor datasheet rather than a device schematic, even though it is catalogued as one. JIS designations starting with 2SC refer to NPN bipolar transistors. Open it in any PDF viewer to read the pin assignment, maximum ratings and characteristic curves needed when testing junctions or selecting an equivalent. Components are often marked C3987 without the 2S, so verify marking and package 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.