RAR archive about 2.17 MB named for the X1 Carbon of 2012, the first generation of that ultrabook line. The name does not list the contents, which may be a schematic, a boardview or both, so extract it with WinRAR or 7-Zip and review the files. Such documentation is used to trace power rails, locate components and test points, and work through shorts or no-power faults on the mainboard. Since later X1 Carbon generations use different boards, confirm the board number printed on the PCB matches the material inside.
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.