In Adobe Flash Builder click the File menu, then Export.

On the Export window expand Flash Builder in the export destination list, then click Release Build, then click Next

On the Export Release Build window select your target platform.

Click the "Signed packages for each target platform" option

Click Browse and specify an export location for your application, then click Next.

On the Packaging Settings window, Digital Signature tab, click the box next to "Enable digital signing", then click Finish