Thursday's match in Austria was the first of three warm-up games for Volker Finke's men before the tournament in Brazil, which starts next month.
However, Cameroon - who missed a late penalty - were left in no doubt as to the difficulty they will face in South America, as goals in each half from Oscar Romero and Roque Santa Cruz ensured victory for Victor Genes' men
With Finke yet to trim his squad down to the maximum size of 23, several players with limited experience were handed the opportunity to shine.
But they were on the back-foot from the off as Romero opened the scoring with a composed finish inside four minutes.
Santa Cruz swept home the second with just over 20 minutes remaining, before Eric Maxim Choupo-Moting halved the deficit.
There was late drama when Cameroon were awarded a spot-kick, but Mohammadou Idrissou fluffed his lines from 12 yards.
Paraguay - who failed to qualify for the World Cup - attacked from the off and were celebrating an early goal when Ramon Coronel burst down the right before his centre was collected by Romero, who took one touch before calmly finishing past Charles Itandje in the Cameroon goal.
Santa Cruz went close to extending the lead when he flashed an effort wide of goal with 20 minutes on the clock.
Both teams shared a chance apiece shortly before half-time, Benjamin Moukandjo's free-kick was well parried by Paraguay keeper Roberto Fernandez, while Itandje's foot denied Romero a second when the forward went one-on-one.
Cameroon started the second half brightly, yet it was Paraguay who thought they had doubled the lead when David Mendieta put the finishing touch on a well-worked move only to be denied by the offside flag.
Paraguay did grab a second in the 68th minute, however, when experienced Malaga striker Santa Cruz side-footed home first time from Junior Alonso's cross.
Choupo-Moting pulled a goal back with 15 minutes remaining after he smashed home from close range following a bout of head tennis at a corner.
Cameroon were then handed a lifeline when Moukandjo was clumsily felled by Gustavo Gomez in the area, but Idrissou saw his penalty saved by Fernandez, leaving Finke with much to ponder before their World Cup opener with Mexico on June 13.
