Datasheet PDF of 60.8 KB covering the 2N3904, one of the most commonly found JEDEC part numbers in general-purpose circuits. The index lists it among schematics, but the content should be single-component data. It helps a technician identify leads, check limits against the circuit's supply rail and pick a substitute from stock. Packages and pin orders can vary between manufacturers and case styles, so match the physical part to the outline drawing before soldering anything in place.
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.