Your temporary evaluation or extension license will only last for a certain amount of time. However during this time you can continue to use the product freely. Choose this option if you do not want to either purchase now or enter your new license details at the moment, but just wish to keep using a trial copy of the product.
If this option is not available then you must register, or, if you have already done so and have received a new license, you can enter your new license details to reactivate the product.
See also: Overview, Trouble-Shooting, Purchasing Options, Purchasing Methods, License Installation