The 72-year-old was leaving through the front door of a house on Widdows Street in Leigh when he was approached by a man at about 2.30pm on Thursday (Dec 15).
The man started to talk to the victim about guttering when he grabbed hold of his black Puma bag.
The victim - who did not want to let go of the bag as it contained important documents - ended up on the ground and the robber ran off into a waiting car.
A witness who ran over to help the victim believes the offender came from Mill Lane Street and saw him get into a blue BMW get-away car which was parked on the junction of Brideoak Street.
The car was then witnessed speeding off towards Chapel Street.
The offender is described as white, in his mid to late twenties, around 5ft 10ins-tall, and of medium build.
He was thought to be wearing a black cap, grey jacket with a yellow badge on the left sleeve and dark trousers.
Detectives found a white builder-style glove at the scene and it is thought the offender may have been wearing it at the time of the attack.
Detective Constable Lynsey Watson-Perry, from Wigan’s CID team, said: “This was a heartless attack on a vulnerable, elderly man who was just going about his to day-to-day business.
“Luckily he wasn’t seriously injured but he was understandably extremely upset and attacks like this can cause long-lasting emotional damage making people frightened to go out.
“What this man did to him was cold-hearted and callous; the victim was utterly defenceless.
“We are doing everything we can to find the man responsible, as well as anyone who was in the get-away car, but we need witnesses to come forward.
“If you saw anything, or remember seeing a man in the area acting suspiciously beforehand, then please get in touch.
“There would have been quite a few cars on the road with people on their way to pick up kids from school. So if you also saw a car matching the above description, please call police.”
Anyone with any information should call police on 101 and quote the reference number 1243 of 15/12/16, or the independent charity Crimestoppers, anonymously, on 0800 555 111.