Named after the transistor type 2SC4646, this 148 KB PDF most likely contains the part datasheet. No board, model or revision is mentioned. The 2SC prefix follows Japanese JIS numbering for NPN devices, commonly used in RF, switching or amplifier stages. A technician consults it for pin order, package type, voltage and current limits, gain bins and dissipation. That information is needed to test the part out of circuit with a meter or to pick a safe cross-reference replacement. Opens in any PDF reader.
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.