"We thank the judge."
Translation:Nós agradecemos ao juiz.
Ao is actually exactly what it looks like: a + o. The 'o' is the definite masculine article 'the', but in this case, the 'a' is the preposition 'to'.
So 'ao' means 'to the'. The equivalent for feminine objects is a + a = à.
It's a strange construction for English speakers because agradecer doesn't translate directly as 'to thank'. It's more accurately 'to give thanks', which necessitates putting the 'to' before giving the object.
Were those sources specifically about "agradecer"? When thinking about what prepositions and contractions are possible within a given sentence, you need to take into account that some verbs call for specific prepositions and that changing the preposition that comes after can either change the meaning of the sentence or render it incomprehensible.
Agradecer is one of those cases - it doesn't really work with "para".
I don't think there's anything online that's that extensive (only piecemeal explanations for verbs here and there in grammar websites) - if you find one, please let me know :)
Edit: I found this PDF online just now; it's in Portuguese (and by no means comprehensive in term of the number of verbs included), but at least it's something - I hope it helps :)
Sadly that PDF is no longer available.
Here though is one source for a start (for others who come across this discussion):
Sadly, there seems to be no Part 2...
What I find, is the more I look, the more complicated prepositions with verbs seem (for instance para is also stop). So I am taking it slow, and not looking ahead.
But if I find more resources, I will try to add them here too. :)
In that case it is not correct. "Para" i think that will be more used when you give something to someone. For example: "Ela vai dar aquele casaco ao/para o menino".
(She will give that coat to the boy).
In this case you can use both.
Obs.: I am not sure about that, but I think that "para o" cannot be used after a verb in the infinitive...