Reference PDF for the 2N3906, 61.0 KB, a widely encountered JEDEC part number that turns up in many consumer and hobby circuits. Although listed as a schematic, the document should be a component datasheet. It is useful for checking lead order, rated limits and gain figures when a stage misbehaves or a replacement is needed. Different manufacturers and package styles exist under this number, so compare the outline drawing with the actual part on the board before relying on the pinout.
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.