You said to him, " Did he file the case to secure his rights".
You said to him, " Did he file the case to secure his rights".
Explanation
If reported verb is in Past Tense, reported speech will change from Past Indefinite Tense to Past Perfect Tense. I said, “He went to Calcutta.” I said that he had gone to Calcutta. Moumita said to Shampa, “I drew a picture of you.”