Power-section schematic, going by the pwr-sch suffix, for equipment identified only as BFI, an abbreviation the name does not explain. The 921 KB PDF likely details the mains input, transformer or switch-mode stage, rectification and regulation. Repair work typically starts here: check fuses, rectifiers and filter capacitors, then measure each output rail against the drawing. It is the same size as the Audio Pro AP3000 power sheet, so it may be the same document, though that is not confirmed. Confirm the board matches before relying on it.
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 @pdf_servicemanual. 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.