Catalogued as a schematic, this 117 KB PDF is named 400DMQ035 and states no device, brand or revision. The code resembles a high-current rectifier module part number, so the content is likely a datasheet rather than a board diagram. Look for the terminal arrangement, voltage and current limits, forward voltage curves and mechanical dimensions. Technicians use such sheets when repairing heavy power supplies and choosing a replacement module. Confirm the marking on the original part, since suffixes indicate voltage grade.
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.