I want to see symbols in the disassembly wherever possible, and I have a PDB file for the .exe I'm debugging, but I can't find a way to load the PDB file from disk. Is it even possible?
You can use symload/loadsym command.
In the x64dbg console type:
With the last argument, you can control if the validation of symbols shall be skipped or not (1 - skips).