Please note that you do not need to convert from Version 12 to Version 14.

You need to add the Version 12 company to Version 14.

When you open the company, a message will pop-up with the message that the file must be rebuildrebuilt.

On that message, you need to click "yes,"; the backup message will come up, then you need to run the backup.

After running the backup on the company, then click "yes" to continue with the rebuild.

After running rebuild, then you will be able to open the company.

Please refer to the attached document that will guide you with the conversion.