When you receive your new license key, you need to paste it into the 'License Key' field in the 'Register PerfectIt' dialog found in PerfectIt's 'Help' menu.
You can open this dialog by clicking on the Help menu in the main PerfectIt pane (not the MS Word 'Ribbon') and selecting 'Register PerfectIt'.
The 'Register PerfectIt' menu item in the Help menu (Enlarge image)When the dialog opens, paste your new license key into the 'License Key' field. If the field is not empty, then you must delete the current content before pasting (or select the text and paste over it).
The 'Register PerfectIt' dialog (Enlarge image)Once the key has been entered, click 'Submit'.