Mainboard schematic in PDF for a device named QBOOK-3G, apparently a compact notebook or tablet with a 3G modem variant. No board number, revision or manufacturer appears in the name, so identify the hardware from its PCB markings first. A schematic of this kind shows power rails, charging and battery circuits, modem and SIM wiring, and component references for diagnosing shorts or dead boards. Any PDF viewer opens it. Compare chip markings and connector layouts with your board before trusting the circuit values 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 @ITHINKHS. 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.