Benedict, before leaving the papacy in February, passed on a draft of the encyclical, "Lumen Fidei (The Light of Faith)" for Francis to complete, ANSA reported.
"It's an encyclical written by four hands, so to speak, because Pope Benedict began writing it and he gave it to me," Pope Francis said.
The encyclical touches on themes such as encounters with Christ and how faith and reason can complement each other, Vatican Radio reported.
Benedict's other encyclicals include "God is Love," published in 2006, "Saved in Hope" (2007) and "Charity in Truth" (2009).
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