Combined PDF of 49.6 KB whose name covers both 2N5550 and 2N5551, followed by a trailing 3 that may be an edition number but is not explained. Catalogued as a schematic, it is most likely a shared datasheet for two related JEDEC discrete parts. No board or device is stated. Such a sheet lets a technician compare the two variants side by side, check pinout and package, and see which ratings differ. Confirm the exact code printed on your part before choosing values from the table.
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.