I’m just learning about networking, and have a few questions regarding packet forwarding.

When a packet is traveling through a network to reach a destination host, does the source and destination IP addresses in the packet change? More specifically, does each router that grabs the packet, update the source IP address to itself before forwarding it? If so, how does the destination host send an acknowledgement back when it doesn’t have the original source host IP address?

Thank you all in advance.