With the name 1N756A and a size of 50.3 KB, this PDF appears to be the datasheet for a single JEDEC 1N diode type in its A grade, filed under schematics. It is the first of four consecutive same-sized files up to 1N759A. Technicians refer to it for rated values, tolerance, cathode band position and dimensions when diagnosing a circuit or ordering a replacement. Any PDF reader displays it; confirm the printed code on the part first, since related numbers share the same package.
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.