The DNG format is a format for raw camera images. The Digital Negative (DNG) format stores uncompressed data. Several cameras capture DNG files directly, and many applications can create them.
Install the Free Adobe DNG Converter
This versatile utility is free and can easily convert your images to DNG files which Radiant Photo can easily open. This method is very reliable.
For best results, click the Change Preferences button and set the Compatibility to Camera Raw 7.1 and later.
Download for free here – https://helpx.adobe.com/camera-raw/using/adobe-dng-converter.html
Try DxO Pure Raw
Looking for a robust DNG converter that can create DNGs with lens correction and noise reduction? DxO PureRaw works quite well and can easily hand off its files to Radiant Photo.
You can download a trial version or purchase it here – https://www.dxo.com/dxo-pureraw/