psdx to jpg conversion represents export of Adobe Photo Touch graphics files (.psdx) to standard JPEG format, typically to share the pictures with users that do not have access to Photoshop / Photoshop Touch.
As is typical for unique formats, it can only be saved using the original software, so if you do not have access to Photoshop yourself, you will have to ask the person that send you the .psdx file to export it as .jpg file for you.
Updated: October 24, 2023