Named 2SD1350_E, this 44.0 KB PDF sits in the schematic category but most likely holds the datasheet for the 2SD1350, an NPN low-frequency bipolar transistor under Japanese JIS numbering. The trailing _E possibly marks an English version, which cannot be confirmed from the name alone. Technicians consult such a sheet for base, collector and emitter layout, voltage and current limits and hFE range. Check that the package and marking of the part on the board match before relying on it.
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.