Can cooking food from a packet that has fallen on the floor cause food poisoning if cooked on low heat? if you handle the food after touching packet?

Unlikely: Of course it depends somewhat on the floor it falls on. Cleaning off food that has fallen and then cooking it should protect against food poisoning but then there are some floor you can eat off and some that you would not want to. Evaluate the floor, clean the food and then cook it thoroughly and you should be fine. Otherwise, maybe you need to discard it.