If you have checked for foreign objects such as burrs, wood, glass or anything that could get under the paws and have not found anything it could be few other things.
Find a room with a bright light and put a towel down for your dog to lay on. Use a blunt nosed scissors and trim the hair between the pads.
This will help you look for any foreign object and help clean the foot. Be really careful when cutting because a dogs foot is very sensitive and if you mess up he will never let you look at his feet again. Look for any splinters or stickers in between the feet.
If you can find something you can remove, do so with care. Your pet might start to stress out. You can tell if your pet is in pain or in stress if he starts to pant or tremble. If it's too deep to take out yourself take him to the vet. Then it's not you he's afraid of. Who wants our pets to be afraid of us? Not me!
If you are able to remove the object wash the paws with a very mild soap like baby shampoo and apply a soothing ointment. Oatmeal is very soothing as is Aloe Vera. Find a product with either of these ingredients. Aloe Vera is very powerful in treating cuts and infections. You can find some soothing salves at the pet store.