The 84-year-old actor is releasing his memoir, Sonny Boy, later this month and 15-month-old Roman - who he has with Noor Alfallah - was one of the reasons why he wanted to write the book.
The Scarface star - who also has three adult children from previous relationships - told the New York Times newspaper of his little boy: "He's come into the world a little more now. He's learning things."
Asked if writing his story in his own words for Roman was one of the reasons for writing his book, he said: "That's one of the reasons, of course. And that has been a campaign for me to stick around a little longer if it's possible."
But Pacino isn't sure if his own advancing years were a motivation for having another child.
Asked if it is possible "that having a child at 83 years old is a reaction to the recognition of your own mortality?", he replied: " Wow, that was something. I have to really think about that. I don't know. Maybe? I don't even understand it."
However, Pacino admitted having his young son has given him a "different" perspective on life.
He said: "When I saw the little baby there and the way he was just - you look at it differently now. You look at it like, what is this? This is so amazing!Â
"That's why I was so excited by hearing the Big Bang. Because I thought, I'm not gonna die!
"I don't mean literally. I mean spiritually. There's something out there that's bigger than us! You can't say 'better', because you don't really know, but something's out there going on that's more than we understand."
Elsewhere in the interview, the veteran actor was asked what movie Roman should watch one day to grasp a sense of his talent and suggested 2011 comedy Jack and Jill, in which he played a fictional version of himself appearing in a Dunkin Donuts commercial.
He said: "I think he should start off with Adam Sandler's.
"... That's funny. It came at a time in my life that I needed it, because it was after I found out I had no more money.
"My accountant was in prison, and I needed something quickly. So I took this.
"There's this thing I do in that film: They got me doing a Dunkin' Donuts commercial. You know how many people think I actually made that commercial? I mean it's just so unfair."
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