The stars were at the Macworld Expo discussing the biopic "jOBS," set for release in April and recently screened at the Sundance Film Festival.
Kutcher an Internet technology entrepreneur and investor plays the late Apple co-founder Steve Jobs while Gad took on the role of Steve Wozniak, the engineering wizard of the duo whose accomplishments changed the way people live.
"I wanted this story told in a way that honors my hero," Kutcher said. "I had never played someone who had lived before and was somewhat terrified by the notion."
Steve Jobs' legacy is so great that theatergoers are likely to use their own memories to rate the actors, Kutcher reasoned.
"It's not like you are playing (Abraham) Lincoln," he said in reference to the former US president. "We don't have a lot of video of Lincoln, but we have a lot of video of Steve."
"And we have a lot of daily reminders of him at our fingertips," he continued in a reference to iPod, iPhone, iPad gadgets introduced by Jobs prior to his death in late 2011," he said.
"Playing that guy who everyone has a memory of is really scary."
Gad, meanwhile, admitted knowing little about either Jobs or Wozniak before taking on the project.
"I was as computer illiterate as Steve Wozniak was computer literate," Gad joked, saying he took programming classes to prepare for the role.
The film focuses on the life of Jobs from when he dropped out of Reed College in Portland, Oregon, in the early 1970s, to when he introduced the first iPod MP3 player in 2001.
To prepare, the actors met with people Wozniak and Jobs knew in those years and shot some of the movie in the Silicon Valley garage where the first Apple computer was created.
Kutcher and Gad told of immersing themselves in their respective roles for months, saying the movie is meant as a reverent interpretation of the story that captures the essence of who the men were and what they did.
Kutcher said he even went on a fruit-only diet Jobs had tried, only to wind up "doubled over in ridiculous pain" and hospitalized with pancreatitis.
"I learned everything I could about Steve (Jobs)," Kutcher said. "I walked around repeating everything he said to other people, because he said enough brilliant things that you sound like you really are brilliant."
Gad compared the story of Jobs and Wozniak to that of famed Beatles band members Paul McCartney and John Lennon.
"That these two would meet and it would be this perfect storm fascinated me," Gad said.
Kutcher told the packed auditorium that playing Jobs changed his life.
"Don't settle for what life gives you; make life better and build something," Kutcher said.
"That passion and dream and understanding that you can be part of something that makes people's lives greater was the essence of who the guy was and that really affected me."
In recent news reports, Wozniak trashed the film based on what he has seen of promotional clips and the script.
"I hope that when he sees the movie in its entirety he will understand we went to great lengths to capture the essence of his journey," Gad said when asked about the criticism. "It was done with the utmost love and respect."
Jobs had been a crowd-drawing headlining speaker at the annual gathering, expected to draw 25,000 people by the time it wraps up Saturday, where he unveiled Apple innovations such as the iPhone with a trademark "one more thing" line.