PDF schematic of a 150 W amplifier, marked as a new version and converted from another file format, judging by the name. No brand, model or revision is stated, so identify the circuit by comparing it with the board on the bench. At 4.41 MB it may contain several pages or high-resolution images. Technicians use such diagrams to follow the supply rails, check the differential input, driver and output transistor stages, and verify resistor and capacitor values before replacing burnt parts. Any PDF reader will open 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.