Given some Random.exe
on Windows, how can I determine
Is there a property in File Explorer, some other tool, or programatic method I can use?
The architecture of the executable is written in the Machine field of the COFF header. You can retrieve it programatically or manually with a hex editor:
You can see PE structure here. The valid Machine field values are listed here.
EDIT: Here's a C code that does that, untested:
int main(int argc, char *argv[]) {
FILE *f = fopen(argv[1], "rb");
uint32_t offset = 0;
fseek(f, 0x3c, SEEK_SET);
fread(&offset, sizeof(offset), 1, f);
fseek(f, offset + 4, SEEK_SET);
uint16_t machine = 0;
fread(&machine, sizeof(machine), 1, f);
printf("Machine: 0x%.4x\n", machine);
}