General information about Pixhawk designs, schematics, reference hardware, FMU versions, licensing, and trademarks, and contributing to the project can be found in the repo README.
The open hardware design of Pixracer (based on FMUv4) is provided here.
The design is provided in Altium Designer CAD files.
It consists of schematic files (*.SchDoc), BOM listings, and includes open reference hardware PCB layouts (.PrjPcb).
Tip PDF versions of the schematics and PCB layouts has been made available for easy previewing (i.e. if you don't have Altium Designer).