Is it forbidden to sell baby food that contains pork, and is it obligatory for someone who works for a company that sells such products to leave their job?

If your work is free from selling foods containing pork or forbidden goods, or from indicating them, then there is no harm in continuing in it, though it is better to search for work that is free from prohibitions and doubts. However, if the work involves anything of what was mentioned, then it is not permissible to continue in it, and it must be abandoned.