No matter how far along your pup is in potty training, they will need time to get acquainted with the new space and figure out where they can go. They need to feel comfortable, and because they are absorbing a completely new environment, you may find your pup having accidents in corners of your house where he can be alone and feel safe. Do not discipline them or punish them for this. This is completely normal, and again, the priority is giving them a safe space and teaching them where to go.
Also, a personal preference and choice was for me NOT to use puppy training pads. This is because dogs use touch and smell, and guess what feels like a puppy pad? Your cotton t-shirts or your soft blanket! What we found much more helpful was using fake grass pads, since the color and texture emulated grass. The grass pad was much easier to clean too, just hosing off with water and reusing (so it is more eco-friendly than a disposable pad).