The ceremony was attended by dignitaries such as Prime Minister John Key and leader of the opposition David Shearer.
Sir Paul had been treated for prostate cancer earlier in his career but it returned early last year, putting his work on hold. Last June he also underwent open-heart surgery.
Following the surgery, Sir Paul wrote a personal account of what he had been through.
"I couldn't speak. Not with the half-inch pipe down my throat. I couldn't sleep. Not for days. The staff urged me to try. But when I closed my eyes I saw only nightmare visions. It was unbearable. I was exhausted."
Sir Paul briefly returned to the country's screens and airwaves, but in December announced he was retiring from broadcasting.
After his investiture, Sir Paul said the cancer had sparked other health problems, such as suffering from hayfever for the first time in his life.
"The old cancer found me out and has started to do some funny things."
He also spoke of his grim health problems.
"We still have a lot of fun, a lot of good times, but soon realities have to be faced ... We haven't had a chance to meet with the doctor to discuss what's going on, but I don't think it's flash.
"I don't think Houdini will do it this time."
Sir Paul has survived a car crash, fatal helicopter accident, light aircraft crash and previous illnesses. He had been looking forward to retiring in his Hawke's Bay home.
"The plan was I would build this farm and retire here, and live a long and wonderful life basking in my former great career," he said.
"But along comes the bloody [illness]."
