PDF titled only with the part number D304X, about 489 KB, filed as a schematic. The name gives no further detail on device type or manufacturer, so the contents are most likely a component datasheet for that marking rather than a circuit diagram. Technicians typically open such a file to confirm pin functions, ratings and package outline before testing or replacing a part. Compare the full marking and package on the board with the document, since short markings are easily shared by unrelated parts from different makers.
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.