That depends on what you consider to be official church teaching, at least today.
No one shall join in prayers with heretics or schismatics. – Council of Laodicea, can 29; http://www.newadvent.org/fathers/3806.htm
If any Bishops or Priest or Deacon shall join in prayer with heretics, let him be suspended from Communion" - not found yet: III Council of Constantinople [attribution unverified].
“the Church forbids the faithful to communicate with those unbelievers who have forsaken the faith they once received, either by corrupting the faith, as heretics, or by entirely renouncing the faith, as apostates, because the Church pronounces sentence of excommunication on both.” St. Thomas Aquinas, Summa Theologica; http://www.newadvent.org/summa/3010.htm
"One must neither pray nor sing psalms with heretics, and whoever shall communicate with those who are cut off from the communion of the Church, whether clergy or layman: let him be excommunicated". (Council of Carthage [not found]
Rome, Italy, Feb 19, 2010 / 02:03 pm (CNA).- The president of the Pontifical Council for Promoting Christian Unity, Cardinal Walter Kasper, announced this week that Pope Benedict XVI will visit the Evangelical Lutheran Church located in Rome on March 14 for an ecumenical celebration.
ISTANBUL – Pope Francis stood Saturday for two minutes of silent prayer facing east in one of Turkey's most important mosques...His head bowed, eyes closed and hands clasped in front of him, Francis prayed alongside the Grand Mufti of Istanbul, Rahmi Yaran, in the 17th-century Sultan Ahmet mosque. -http://www.freep.com/story/news/world/2014/11/29/turkey-pope/19661965/
Other things RCs are unlikely to be aware of, or obey:
We furthermore forbid any lay person to engage in dispute, either private or public, concerning the Catholic Faith. Whosoever shall act contrary to this decree, let him be bound in the fetters of excommunication. — Pope Alexander IV (1254-1261) in “Sextus Decretalium”, http://oce.catholic.com/index.php?title=Religious_Discussions
Commenting on this, the Catholic Encyclopedia states,
“This law, like all penal laws, must be very narrowly construed. The terms Catholic Faith and dispute have a technical signification. The former term refers to questions purely theological; the latter to disputations more or less formal, and engrossing the attention of the public....
But when there is a question of dogmatic or moral theology, every intelligent layman will concede the propriety of leaving the exposition and defense of it to the clergy.
Can. 831 §1 Unless there is a just and reasonable cause, no member of Christ's faithful may write in newspapers, pamphlets or periodicals which clearly are accustomed to attack the catholic religion or good morals. Clerics and members of religious institutes may write in them only with the permission of the local Ordinary. - http://www.intratext.com/IXT/ENG0017/_P2P.HTM
But the clergy are not free to engage in public disputes on religion without due authorization...
That this legislation is still in force appears from the letter addressed to the bishops of Italy by Cardinal Rampolla in the name of the Cong. for Ecclesiastical Affairs (27 Jan., 1902)
Quinisext Ecumenical Council, Canon 64: It does not befit a layman to dispute or teach publicly, thus claiming for himself authority to teach, but he should yield to the order appointed by the Lord,
... But if any one be found weakening [disobeying] the present canon, he is to be cut off for forty days. — http://www.newadvent.org/fathers/3814.htm
* “Do not converse with heretics even for the sake of defending the faith, for fear lest their words instil their poison in your mind.” Bl. Isaias Boner of Krakow (Polish, Augustinian priest, theologian, professor of Scripture, d. 1471)
“...the Church forbids the faithful to communicate with those unbelievers who have forsaken the faith they once received, either by corrupting the faith, as heretics, or by entirely renouncing the faith, as apostates, because the Church pronounces sentence of excommunication on both.” St. Thomas Aquinas, Summa Theologica, Article 9, “Whether it is lawful to communicate with unbelievers?”; http://www.newadvent.org/summa/3010.htm
"Those are by no means to be accounted heretics who do not defend their false and perverse opinions with pertinacious zeal (animositas), especially when their error is not the fruit of audacious presumption but has been communicated to them by seduced and lapsed parents, and when they are seeking the truth with cautious solicitude and ready to be corrected" St. Augustine
Doctrine in canon law cannot be changed. But other things in canon law can be changed.