KB: Compare netlist generated from schematic to that transferred to PCB layout
Solution Details
As a unified environment, Altium synchronizes schematic data with PCB layout behind the scene such that there is no exchange of intermediate text file. Since the ECO does a direct project to pcb compare, there is no native Altium netlist format per se:
https://resources.altium.com/p/understanding-your-pcb-netlist
There is a command to export the netlist from schematics as a text file from Design » Netlist for Project, and from PCB side, Design » Netlist » Create Netlist From Connected Copper', but the two does not follow the same format/syntax/order unfortunately.
Instead, to compare the data between the project (schematics) and a pcbdoc contained directly, invoke Project » Show Differences..., and select the pcbdoc and click OK.
It is also possible to compare across two different projects/documents, by ticking Advanced Mode at the bottom in the dialog.
https://www.altium.com/documentation/altium-designer/keeping-schematics-pcb-synchronized#!displaying-physical-differences