They are synonyms. Abduct / kidnap someone: take someone away illegally, especially using force and in order to get money or something else for returning them.

Sam's answer is the most thorough.

I heard both of them in one movie!!! Abduct : to take someone away by force, especially a child or young person, often in order to kill them or sexually attack them - used especially in news reports for example: The two high school girls were abducted at gunpoint on Tuesday. Kidnap : to take someone away by force and keep them as your prisoner, in order to make their family or their government give you money or other things you want for example: Terrorists have kidnapped a French officer and are demanding $400,000 from the French government. I hope it helps you.

kidnap and abduct, these two words having the similar meaning defined by the dictionary, they are synonyms. But, I have never read the word "abduct" either in written articles or spoken in movies.

We have here again two synonyms Kidnap (someone) = capture, rob Abduct (something) = capture, diverge, rob