.IDDX File Extension
File TypeStatic Default File
What is an IDDX file?
File created by InDesign and InCopy, professional page layout creation applications; contains default document settings; imported by InDesign right before .IDML files to keep consistent document default settings; should not be manually opened or edited.
IDDX files are located in the following directory:
InDesign or InCopy/Presets/Default