Commits each party to sign any additional documents and do any further acts reasonably needed to give full effect to the deal.
Sometimes one signature isn't enough — a registry, a bank or a mutation office may later need an extra form, a correction deed or a fresh signature to make your ownership fully clean. This clause says the other side has to cooperate and sign those *further* papers when reasonably asked, usually at their own cost if the fix is their responsibility. It saves you from being stranded if a loose end turns up after completion and the seller has otherwise moved on.