This is the 757th most frequent Turkish word.
yasal
Legal.
In this sentence, 'yasal' functions as an adjective modifying 'belge' (document), giving it the meaning of being officially recognized under the law.
Yasal belgeyi mutlaka kontrol etmelisiniz.
You must certainly check the legal document.
Here, 'yasal' describes 'bir yolu' (a way), indicating whether a legitimate and law-abiding method exists.
Bu işlemi yapmanın yasal bir yolu var mı?
Is there a legal way to perform this action?
In this context, 'yasal' modifies 'haklarını' (their rights), meaning these rights are established and protected by law.