The file 30WQ03F is a 38.7 KB PDF that, despite its schematic label, appears to be a datasheet for a single rectifier diode, judging from the naming. It probably differs from the 30WQ03FN document only by suffix and revision. Technicians open it in an ordinary PDF reader to confirm forward and reverse characteristics and the package outline when hunting a replacement. Because the name gives no device context, identify the part on the board by its printed marking first and confirm it matches this exact code.
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.