So one of my players took the feat Acrobatic Dodge
Now last session he was hit on a surprise round and I ruked that since the feat states that if he can't take a five foot step he can't use it, he is not allowed to use this on surprise round.
He argued that since he also has uncanny dodge he can't be caught off guard so he should be allowed to use it.
I ruled against, but later I had doubts...
Can you help me decide?
I think the part that says 'If you cannot take your 5‑foot step, you cannot use this feat.' is probably referring to situations like difficult terrain, where you wouldn't normally be able to take a 5' step, or if you're immobilized for some reason.
Reading it over, I think I'd agree with your ruling, but for a different reason.
You can use a swift or immediate action any time you could use a free action (page 188). On page 178, it says 'Combatants who are unaware at the start of battle don't get to act in the surprise round'. Uncanny Dodge doesn't change that, it just removes the flat-footed part of it from the next sentence. Since they're unable to take any actions at all (even if they're free), they don't have an immediate action available to them to use the ability.
You can 5foot step in a surprise round and he cannot he flat footed, he would have an immediate action and he would lose his swift from his next turn. He doesn’t need a turn in the surprise round to lose the next turns swift action that just happens whenever his next turn occurs. So I would of allowed it
Immediate actions specifically say you can't use them if you are flat footed, which pretty much means that not being flat footed means you can use one (assuming you haven't already etc.)
Uncanny dodge or Combat reflexed also lets you take attacks of opportunity when flat footed, an are specifically called out as doing so, so it is unlikely that the phrase 'Combatants who are unaware at the start of battle don't get to act in the surprise round' is a rule that would require specific text to override for any sort of action rather than meaning you don't get a turn (and of course you are flatfooted which prevents off-turn actions.)
If Foeclan's reading was correct, even though Combat Reflexes feat says you can attacks of opportunity while flat-footed, in reality you couldn't (in the vast majority of cases) since Combat Reflexes only allows you to make AoO while flat-footed but doesn't remove the unaware at the start of battle phrasing. That is clearly not the case.
So, you were wrong. Uncanny Dodge means you can take an immediate action during a surprise round.