Datasheet for the 2N3859A in a 59.0 KB PDF, the A suffix forming part of the registered part number as given in the name. It sits in the schematic category but should contain single-device information: pin order, package drawing, maximum ratings and electrical characteristics. Repair technicians use it to check a suspect part out of circuit and to judge whether a substitute will fit the application. Match the marking on the board component, including the suffix, before relying on the listed values.
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.