Even with IDML, you may encounter issues. Here’s a troubleshooting table:
If you have access to the version of InDesign that created the file (or a newer one), follow these steps: Open the file in your current version of InDesign. File > Save As File > Export InDesign Markup (IDML) from the format/type dropdown menu. how to convert indesign file to older version
To convert an Adobe InDesign file ( .indd ) to an older version, you must export it as an file. This format is designed for backward compatibility and can be opened by InDesign versions from CS4 through the latest Creative Cloud versions. How to Convert Your File Even with IDML, you may encounter issues