Datasheet for the 1N4454 diode, a very small 19.5 KB PDF that probably holds a short single-page summary. The 1N4454 is a small signal switching diode in a glass package, similar in role to the 1N4148 family. The document helps a technician check reverse voltage, forward current and recovery time when selecting a replacement for a signal path, clamp or steering diode. Any PDF viewer displays it, and the cathode band and package outline should be checked against the board before fitting a substitute.
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.