PDF schematic labelled 331-1-4-01, with R20 likely giving the revision, about 1.09 MB. The name has no manufacturer or model, so the title block inside is the best guide to what board it describes. Technicians use such drawings to trace supply rails from input to load, check components around a short and follow control signals between ICs. It opens in any PDF viewer. Make sure the board code and revision on the physical PCB match, because similar numbering can cover different products.
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 @hrtechno. 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.