Once you have installed a motor to your kayak most states require it to be registered. Some states even require a boating safety certificate or a boat license to operate a motorized kayak as it qualifies as a motor boat.
The first step after purchasing your kayak is to obtain the Manufacturers Statement of Origin (MSO). Simply call your kayak manufacturers customer service or ask your local kayak dealer. Have the serial # ready. It is typically located at the Starboard Stern or Rear Right side.
You will also need to have a copy of your purchase receipt or invoice. Some states collect sales tax if it wasnt paid at the purchase time. This can happen if purchased as a private sale or within a Tax Free state.
A great resource for information to register your kayak within the state you reside is at www.takemefishing.org. Follow this link for state by state information with a breakdown of documents needed. https://www.takemefishing.org/register-a-boat/#stateList