PDF exported from a CorelDRAW file for a Zener stereo amplifier rated 400 W, 642 KB in size; the Spanish name says it comes without the circuit diagram. It is therefore most likely a PCB layout or artwork rather than a full schematic. Builders use such artwork to make or check the printed board and to locate component positions during repair. Pair it with the matching circuit diagram from the same series when tracing faults, and print it at true scale if etching.
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.