As per the documentation I am putting the executable in the files section so that it gets copied to {tmp} folder and run during the installation (at the beginning). However the file is never copied. I tested with different files like a simple txt file, different source and destination paths and it’s never copied. Only error I receive is during runtime, “file does not exist” and not much information. I also tried without the external flag and it was still the same.

[Files]
Source: "DriverCDM212364_Setup.exe"; DestDir: "{tmp}"; Flags: deleteafterinstall external