It is a fairly messy and tedious process that most people want nothing to do with.
There are no silk screen layers (the white letters/numbers) on the board, so the very first thing you need to do is make good scans of both sides and try and identify what each and every part might be, otherwise a schematic is just going to be a massive mess of components that have no Rx, Cx, Ux, ect., ect., values to compare to the parts on the board.
After you have made up all of the board designators, then you can either strip the board of all the components, or remove them one at a time and measure as many as possible so the values can be added to the schematic. That is very helpful, but it is also massively time consuming.
Once you are down to a 'clean' board (just the PCB with no components on it) get good scans of that also. Then the top and bottom Mask layers (the green/blue paint) can be removed with some light sanding to expose the copper traces. Then you get good scans of that, again.
If the board is multiple layers, and the DS4 controller all are, then the top and bottom layers need to be removed to expose the Inner layers, and that can be done multiple ways. Hand sanding, a Dremel and huge pile of sanding discs, or even a CNC could be used, but that's a bit overkill for a controller PCB. Every method is time consuming and messy. You don't want to get down to the actual copper of the inner layers, as they are half the thickness of the top/bottom layers, so they can and will disappear very quickly if you are not watching watching you are doing.
After the top/bottom layers have been removed enough to where you can see the Inner layers, get good scans of that as well. You can also oil up the PCB at this point so the Inner layers are easier to see, and again get good scans.
After you have all of the layers scanned, it's just another long and tedious matter of picking some starting point and then tracing it out to everywhere it goes. You can put all of the layers into some app like Photoshop or the like so you can reverse half of the layers and kind of digitally rebuild the board for tracing it out and marking things to keep track of what you have and have not done yet.
There are loads of PCB apps out there to make your schematic in, and none of them will make the actual work of stripping the PCB down any easier. I use DipTrace, but again, any of them will do the schematic/PCB part of it once you also figure out how all of that works.
