Paperback, written in English, from 1960s or 70s.
Starts off with a man waking up in cave or buried chamber. He receives info and instructions from a A.I. super computer . (Its been xx years 30? 60? 100? since the collapse of society. The computer's scanners (Satellites? Camera?) are not working anymore and it needs him to scout around and find out whats happening, return, and report back to it what he finds.
Unbeknownst to him, his body has been modified to assist him in surviving, and he has no knowledge of anything from before he awoke. He is stronger, has more stamina, needs to eat less often, and armored bones? (I believe at one point he gets shot but only gets a serious flesh wound, instead of a critical injury because the bullet bounces off a rib instead of penetrating his chest cavity)
Three things I remember from the story.
Shortly after starting his exploration, he rescues a woman being abused by a couple men (Kills them). She follows him for protection. He is not interested, but eventually allows it.
At one point they are stuck in a blizzard, (Maybe also fell through the ice into a river) They are freezing and it is taking to long to gather materials and start a fire. Suddenly his neck locks straight ahead, his jaw opens wide, a tube from his throat sticks out, and a flamethrower or laser shoots out igniting the wood he has gathered into a roaring fire.
They come across a dome? or underground bunker? inhabited by technologically advanced people. (I think they were descendants from American Indian tribes?) They spend the winter with them. The people there do x-rays and tell him that his body is highly modified. [I think #2 happened right at the entrance of the dome/bunker and the energy discharge of lighting the fire is what let the people inside know that someone was outside.]
I believe he addressed/referred to the computer as "Machine"
It is possible the word Machine was in the title. (i.e. "Machine's Man" or "Working For the Machine".)