The existence of this document will help you close the sale of your home, if any questions should arise regarding the competency of the workmanship. Make sure you check with your contractor and have the permit posted on the jobsite. This is required by law.
If you did not make sure you had a licensed contractor do the work, there probably was no building permit issued. If you do not see a building permit posted by your contractor, call your local jurisdiction to inquire if a permit has been issued.