Yes, the longest subscription is a year. Once you purchase a Pro subscription, you can use that for ever and put it on as many computers as you want. The only thing that you won't get after the subscription expires are the updates and tech support. So if you don't want to repurchase in a year, you don't have to, and you will still have a Pro Version.
You will need to Backup the Pro installer either on an external HDD or you could Burn it to a Disc to preserve the Installer in the event of a catastrophe

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