Datasheet for the 1N5820, a 3 A Schottky barrier rectifier, in a 169 KB PDF indexed as a schematic. The rev2 tag marks the document revision, and the dx suffix probably reflects the issuing vendor naming, though the name does not say so outright. It covers forward voltage, reverse current, surge rating and the axial package. Such rectifiers often sit in switching supply outputs and freewheel paths. Use it to match a replacement and confirm the cathode band orientation before soldering.
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.