ECS A790GXM-AD3 revision 1.0 archive, a fairly large 5.98 MB RAR file. The model name indicates an AMD 790GX based board, and the size hints that the package may hold more than a single PDF, perhaps a full schematic set or extra files, though the name does not specify. Extract it with WinRAR or 7-Zip and review each item. Use any schematic to trace the power-up sequence, VRM and memory rails, and verify that the board revision matches 1.0 first.
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 @IT_SERVICE_WORLD. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.
7-ZipWinRARThe Unarchiver (macOS)