I found that the pitchfork was added for Version 18 that was released for Halloween 2017. That version had a lot of new objects added for that theme.
In the current version 21.2, the only thing that you can do with a pumpkin is to smash it with a mallet to get pumpkin seeds, which you can then plant to get more pumpkins. The pumpkin cannot be used for food in this version.
In talking about the new version being developed, Denki has said in https://denki.itch.io/autonauts/devlog/45847/all-the-worlds-an-autostage "There’s no mistaking who ate all the pumpkin pies here", and he shows a bot taking pumpkin pies from a storage bin and feeding them to a very fat folk.
Also, I asked Denki "How do you carve pumpkins into Jack-o-Lanterns?" and he said in https://itch.io/t/118969/autonauts-faq?before=244
"Unfortunately Jack-o-Lanterns were only active for V18 Halloween :( There isn't anything to make with Pumpkins yet but we'll add that in another version."