Since your vehicle was hit by an animal, a deer, it would appear that you are making a claim through your comprehensive coverage. Part of settling a claim usually includes an investigation of the claim and determining the value of your vehicle.

The insurance adjuster is likely requesting the bill of sale to help him or her calculate the actual cash value (ACV) of your car which was declared a total loss. Normally an insurance company does not find a bill of sale to be a confidential document since one usually must show this at the DMV to pay taxes on the vehicle and obtain your plates.

If you feel that giving the insurance company is an invasion of your privacy or a confidential matter, check with the insurance adjuster to see if it is necessary for their process. If the insurance provider is insistent on getting a copy you may speak with a lawyer or contact your state's insurance regulatory to find out if you legally have to provide them with this information. State laws can differ so this is the best way to find out for certain what you legally need to supply to your insurance adjuster.