At just 39.2 KB, the PDF named 2SC4291 is a compact document filed as a schematic, though the name suggests a brief transistor datasheet. Under the Japanese JIS scheme the 2SC prefix denotes an NPN bipolar transistor, commonly marked C4291 on the part. Even short sheets normally list pin order, package type and maximum voltage and current, which is what a technician needs to identify leads, check the device with a multimeter and select a replacement with suitable ratings.
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.