The 2SB710 named in this 44.1 KB PDF is a PNP transistor by JIS numbering, which suggests a component datasheet despite the schematic category; _E most likely marks the English version. Inside you would expect pin assignment, package outline, collector-emitter voltage, collector current, power dissipation and hFE ranks. Technicians consult it to confirm orientation before soldering, to test junctions correctly for a PNP device, and to judge whether a cross-reference replacement has equal or better ratings than the original part.
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.