They both use the same fault code command which asks the ECU to clear the faults. The pro version has a couple of extra commands for specific ECUs but generally the are both the same for emissions related codes.

This means, that if it is coming back or not clearing, it might be:

* That the fault is not fixed, and it is immediately re-appearing as the ECU knows the fault is still present. Some faults (like a broken sensor) can cause this. Generally cat sensors take a while to trigger, unless something like the O2 heaters are kaput (which is then an immediate code, even if you clear it)
* That the ECUs methodology for resetting the code hasn't been followed. Some manufacturers require the clear code to be sent, then after, the ignition to be turned off (pause) and on again afterwards before the fault registers on the instrument cluster as cleared.

If the fault code is present, then it usually means that the emissions monitors fill fail at least one check (this may differ between manufacturers), so even if the fault code is reset, it will reappear, sometimes immediately as soon as you scan again depending on the type of fault and the test performed. On some vehicles, you may need to reset the fault, *then* turn the engine off/on again for the reset to register in the ECU.

You can do an emissions test in advance, get a certificate that the emissions are in order and they will no longer be examined during the inspection. That's what I did just last week. I don't want to make expensive repairs to an old car if you can just get past the inspection by resetting the fault.
I would just like to reset that fault code myself.
I just wanted to know if the code can be reset, I know everything else that needs to be done.

Resetting the fault code won't fix the problem, and the emissions monitors will be restarted.  In most test centres, emissions monitors need to have fully run before the vehicle can pass the test, meaning that the cat will be checked as part of the emissions monitor test, and will likely fail again if you have not fixed the problem.

So yes, it should reset the fault code, but this will automatically restart the emissions monitors in the ECU, and most test centres won't pass you until those monitors have shown as completed (they are checked as well, as part of the test), and when they complete, if you haven't fixed the fault, then it will show again. 

I have the lite version, it cannot clear the 0420 code.
Can the full version clear this and other codes?I know the catalytic converter is already weak, but by resetting the fault I can still get the car inspected.
The car is a 2005 Skoda Octavia