Schematic in PDF form labelled safari std, a name that in DIY audio circles usually refers to a Safari power amplifier design, standard version, though the file name itself gives no further model detail. At 2.77 MB it likely holds a full circuit drawing or PCB artwork. Technicians use such a document to follow the signal path from input stage to output transistors, identify bias and protection parts, and compare values against a working board. Any PDF reader opens it; verify the layout matches your board before replacing parts.
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.