Paranaense, finalists in South America's top club competition in 2005, play their Group One opener at home to Bolivia's The Strongest in Curitiba on Wednesday night.
"I'm very happy to sign a contract with Atletico Paranaense ... (for) the chance to return to football with the Furacao (Hurricane)," Adriano told the club's website (www.atleticoparanaense.com).
Adriano, who shone at Inter between 2004 and 2009, helping them to win a string of Serie A titles, suffered from injuries and off-field problems in the latter part of his career in Italy and back in his home country.
He last played for Corinthians in March 2012.
Paranaense squeezed into the group phase last week when they beat Deportivo Quito on penalties at the end of the second leg of their preliminary round tie.
"(The Libertadores Cup) is the only title I don't have, and I want to help Atletico win it," said Adriano, who turns 32 next Monday.
He said he hoped to come on as a substitute in his first few matches before competing for a starting place.
Adriano, nicknamed Emperor, helped Brazil win the Copa America in 2004 and the Confederations Cup the following year at the height of his powers as a feared goalscorer.
The group phase got underway on Tuesday, with Argentina's Velez Sarsfield, champions in 1994, winning 1-0 at Universitario of Peru in their opening Group One match.
Holders Atletico Mineiro beat Zamora of Venezuela 1-0 away with a late goal from former Everton and Manchester City striker Jo in Group Four.
Fellow Brazilian side Botafogo beat Argentine champions San Lorenzo 2-0 at the Maracana in Rio de Janeiro in Group Two.
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