Schematic in PDF named only Shiba, a project code name with no brand, board number or revision in the file name. The title block inside should reveal the board maker and revision. A diagram like this is used for tracing voltage rails, locating components and test points, and diagnosing shorts or missing power. At 1.42 MB it is likely a full mainboard set; compare the internal project name and revision with the PCB before working from 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 @afsschematicfree. 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.
Any PDF readerSumatraPDFFirefox / ChromeFlexBV (links PDF to boardview)