N.H. Rev. Stat. Ann. § 657:18

Upon receipt of an outer envelope or an affidavit envelope purporting to contain an official absentee voting ballot, the clerk of the city or town shall, subject to RSA 657:16, attach thereto the application for an absentee ballot to the envelope submitted by said voter and record the information pursuant to RSA 657:15. The envelopes shall be preserved unopened until processed in accordance with RSA 659:50.