Catalogue entry for 2N6784, a 131 KB PDF filed under schematics though its name is just a JEDEC semiconductor part code. No product or board details are given. The contents are most probably a datasheet describing ratings, electrical characteristics and the package. It is handy for identifying pins before testing, interpreting measured values, and validating a replacement. Cross-check the case type and printed marking on the faulty component so the data actually applies to the part in hand.
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.