Searching for a "fixed" license key—often a term used in pirate communities for cracked versions—exposes your system to several threats:

If you have an active FineReader 15 subscription, you may be eligible for a free upgrade to FineReader 16 through your ABBYY account. How to Activate Your Official Key

Once you have a valid serial number, follow these steps to "fix" your installation into a full version: ABBYY FineReader Activation

Many cracked versions of FineReader 15 suffer from crashes or missing features, such as the inability to save recognized text or export to external applications.