From the 2004 Instruction Redemptionis Sacramentum:
"[62.] It is also illicit to omit or to substitute the prescribed biblical readings on one’s own
initiative, and especially “to substitute other, non-biblical texts for the readings and
responsorial Psalm, which contain the word of God”. [footnote 138:
Missale Romanum, Institutio Generalis, n. 57;
cf. Pope John Paul II, Apostolic Letter, Vicesimus quintus annus, n. 13: AAS 81 (1989) p. 910;
Congregation for the Doctrine of the Faith, Declaration, Dominus Iesus, on the unicity and salvific universality of Jesus Christ and the Church, 6 August 2000: AAS 92 (2000) pp. 742-765.]"
From 2002 GIRM n. 57: “… Moreover, it is unlawful to substitute other, non-biblical texts for the readings and responsorial Psalm, which contain the word of God.”
But note that at the Easter Vigil the Roman Missal’s rubrics for that Mass have: “23. … Instead of the responsorial psalm a period of silence may be observed.” (Roman Missal, Catholic Book Publishing Co., New York, 1985, page 187).