Datasheet for a part marked D304X, provided as a 924 KB PDF. The file name gives no description of the component category or manufacturer, so the document itself must be checked to see whether it matches the device on hand. Datasheets of this kind normally include absolute ratings, electrical characteristics, typical curves and package drawings with pin numbering. Use it to identify pins for in-circuit measurements and to evaluate replacements, confirming that markings, package and any suffix letters agree with the actual part.
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.