If you have no license, You can't use this feature, Please Click the "Go to the Microsoft APP Source" link and subscribe. If subscribed, Click the "Refresh" link to reload
Click "Watermark" tab
Import image, input hide text and click "Hide" button. Now, you can export the encoded image buy click "Export Hided"
You'll get the hide text after import encoded image
You can use it in message extension to view image file with ".png" file extension.