If you already own a key, use it. If you need to buy one, weigh the cost (legitimate keys run $80–150 today) against Microsoft 365 Family ($69.99/year for 6 users) or the free alternatives like LibreOffice or OnlyOffice.
Third-party software like Belarc Advisor or ProduKey may help extract keys from older registry files or backups. product key office 2013 professional plus 64-bit
directly to request a replacement or reissue of your lost product key. Official documentation on where to enter your product key If you already own a key, use it