I have just learned that my father is very indebted. To protect myself, can I already renounce his inheritance before his death?

No. Articles 720 and 722 of the Civil Code state that "inheritances open upon the death of the deceased" and that "all agreements aimed at creating rights or renouncing rights to all or part of an unopened inheritance or any of its assets only take effect if authorized by law." Early renunciation of an inheritance is not permitted by law. If you wish to renounce your father's inheritance, you must wait until his death.