Schematic PDF for a Lenovo ThinkPad mainboard numbered 19770-1, a 2.86 MB document. Five-digit numbers with a dash suffix like this follow Wistron's board numbering, and Wistron builds many ThinkPad boards. The diagrams let a technician follow the power-on sequence, find rail names, regulator circuits and signal paths, and look up component values when replacing parts. Open it in any PDF reader and pair it with the matching boardview, checking the board number printed on the PCB 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 @cynetitsolution. 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.