PDF sheet of about 42 KB for the 3N259, catalogued under schematics though the file name is simply a JEDEC part number. Parts in the 3N series are registered four-lead devices, and the matching file sizes of 3N253 through 3N259 suggest a common family datasheet covering several grades. Expect pinout, ratings and characteristic tables rather than a board circuit. Use it when identifying or substituting the component, and verify the exact suffix and grade printed on the package before ordering.
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.