When you launch a trial version, a screen shows the number of days remaining for the trial to expire. On this screen, you have an option to enter a serial number.
This information does not apply to the version of Adobe Premiere Elements available in Mac Application Store.
Use the serial number you have received to convert the trial version to a full version.
Usually, you can find the serial number on the back of the CD or DVD case. If you have an envelope for your software, the serial number can be on the envelope instead. The serial number starts with the number 1057: