Archive covering the X450LD mainboard, revision 1.1, packed as a RAR of about 1.12 MB. The file name gives no hint of its contents, so open it with WinRAR or 7-Zip and check for a schematic or boardview. Documentation like this is used to trace power and signal nets, find test points and identify components around the charger, VRM and other circuits. Newer revisions 2.0 and 2.1 of this board are documented separately, so compare the revision on the PCB with 1.1 before relying on the layout or values.
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 @alischematics. 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.