The 8ETU04 document, a 187 KB PDF filed as a schematic, carries a part number in International Rectifier and Vishay rectifier style. Expect datasheet content: maximum reverse voltage, forward current, recovery behavior, pin assignment and package outline. Technicians open it in a PDF reader when a fast rectifier in a switching supply or PFC stage fails and a correct replacement is required. Since recovery speed matters in such circuits, substitute only with a part of equal or better rating and verify the original marking.
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.