Another copy of the 2N5401 datasheet, a 49.2 KB PDF whose _3 suffix probably marks an alternate version or a third saved copy rather than a documented revision. The file name does not identify the issuing manufacturer. The 2N5401 is a high-voltage PNP transistor often paired with the NPN 2N5551 in amplifier and line-driver stages. Technicians read it for pinout, breakdown voltage and gain figures when replacing or substituting a part. Compare it with the other 2N5401 sheets if pin assignments seem inconsistent.
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.