Extract Circuit Diagram from Existing PCB Board and use these documents for PCB reproduction, circuit diagram normally include layout drawing, Gerber file, BOM list and schematic;
Master the basic framework, take the similar PCB Board as reference when extract circuit board wiring diagram:
For those basic formats of electronic PCB Board circuit diagram drawing, engineer should understand them very thoroughly, because they can help to draw some simple and typical circuit unit directly, but also form electronic circuit framework.
From other side, please remember that same kind of electronic product can be similar to a certain extent, engineer should accumulate more experience and can take them as reference to restore schematic diagram from printed circuit board.