If the purchase is made by a couple, you both need to be present for the signature (notaries are extremely reticent about drawing up powers of attorney for foreigners living abroad, or else check with the notary well in advance!).
On the date of signature, or several days later, remember to ask for several certificates of signature of the deed from the notary, you will need them for various formalities.
For further information about acquisitions of properties, consult the headings:
Buy or rent?
Buying with SAFER
“Inventory” of land under tenancy:
For land taken over under tenancy there is an obligation to carry out an inventory within 2 weeks after signature.
More information on leases