Sometimes it's not indoors. - Germany surrenders to France in a railroad car.[1] - France surrenders to Germany in the same railroad car.[2] - Japan surrenders to Allies on the deck of the battleship Missouri. [3] - S. Vietnam surrenders to N. Vietnam, outdoors at the presidential palace.[4] Formal surrenders are rare today. [1] https://www.history.com/.image/c_limit%2Ccs_srgb%2Cq_auto:go... [2] https://4.bp.blogspot…
My understanding is there was no formal handover in 1975. In fact when the N. Vietnam knocked down the gate of the Presidential Palace and went inside, the S. Vietnam Prime Minister said he was handing over S. Vietnam and the response was "You have nothing left to handover at this point".