PDF schematic for a board named G31MXP, roughly 1.29 MB, with no brand or revision present in the file name. The G31 prefix indicates an Intel G31 chipset desktop platform. Technicians use such circuit diagrams to follow power rails from the ATX connector, verify the VRM and memory supply, and trace front-panel and reset signals when a board does not start. Read the title block in the document to identify the manufacturer and revision, and confirm they agree with the markings on the motherboard.
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 @Datalvela_servicios. 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.