Sheridan released the Northern Ireland international at the end of last season after a foot injury restricted his chances at Home Park, but he was invited back for a pre-season trial, with the opportunity to seal a new contract.
And the 32-year-old did his chances no harm with the only goal in a 1-0 friendly win against Argyle's non-league opponents.
Sheridan told the club's official website: "He's been biting at the bit. He's trying to impress me. He hasn't played for a long time. He came on and worked hard, and it's always nice to get a goal.
"It's his first game. I don't want to get carried away just because he scored. I thought he did okay when he came on. It was encouraging.
"He's had a bad injury but he's worked his socks off in pre-season.
"I know what he can do. He knows how to play the game. I've got some good strikers in and around the team and I've got good options to play people up there, and I'm still looking at attack-minded players."