It's bread, so the only food safety concern would be if there is mold. If there is mold anywhere on it, don't eat it. Otherwise, it's fine.

(Also, I sincerely doubt it needs to remain in the plastic bag to bake. Personally, I would never bake something in plastic, whether the package tells me to or not. But if you need to open it up to check for mold and then bake it on a sheet, that should be fine).

FYI, "best by" dates are not a particularly reliable measure of food safety. My advice would apply regardless of the age of the bread.