A compact 32.6 KB PDF for the 2N3773, a JEDEC-registered 2N-series transistor; despite the schematic label it is a component datasheet rather than a circuit drawing. Its small size suggests a short text-based sheet, possibly from a different manufacturer than other copies of the same part number. Repair work uses it to verify pin assignment, voltage and current limits and package before replacement. Since manufacturers publish slightly different figures, read the version that matches the logo on the part you have.
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.