Indexed as a schematic, this 124 KB PDF named 90sq most likely refers to the 90SQ series of Schottky rectifier diodes, so it is probably a component datasheet rather than a circuit diagram; the exact voltage rating is not part of the name. Technicians consult such sheets for forward voltage, reverse voltage, current rating and package outline when testing or substituting a rectifier in a power supply. Confirm the full marking on the diode before choosing a replacement with equal or higher ratings.
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.