Jose Crisanto Gomez was found guilty of kidnapping and extortion.
In 2005, Farc rebels handed him the baby of Clara Rojas, a woman they were holding hostage and who had given birth in captivity.
Mr Gomez looked after the child for seven months before handing him over to a state orphanage, where he stayed until DNA tests revealed his identity.
A court in the central city of Villavicencio overturned an earlier decision to absolve Mr Gomez of the charges.
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