I sent an email to support@irisusa.com along with my existing serial number and asked about what update was available to 11.5.x version I had. They sent link to 11.6.3.

After installing, you need to enter serial number and then key.
Below is quote from tech support regarding getting a key.

We need your Machine ID to generate your key.
To get this ID, first install the IRIS software. Then, when you open it for the first time, you will be asked to enter your serial number. Enter it, click Ok and then you'll get the 26-character Machine ID.
Please email us the Machine ID so then we can send you the Key.
You can also get the Machine ID when you click on Register on the Menu Bar (on the top of the screen) and click on Register Wizard.

I have not played around with ReadIris software much now that I use Acrobat. Although I think it does a good job with OCR.

However, I use Acrobat to give me image with text to search. ReadIris can do this as well but the size of the generated file is huge by comparison.

It does not compress or reduce the PDF file size like Acrobat. Example 92 kb 2 page document OCR'd in Acrobat turns into 92kb doc with image and ocr. (Searchable image). In ReadIris, same document turns into 2.8 MB file.