PCB document named VDBL Multi, a 4.16 MB PDF that likely holds layouts for several board variants of a VDBL style amplifier design, as the multi tag suggests. The name gives no power rating or revision. Such artwork is used to locate components, follow copper tracks during fault finding and produce new boards by toner transfer or photo methods. View it in any PDF reader, and when printing for fabrication disable page scaling and check a known footprint dimension so the parts fit the drilled pads.
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.