The most reliable and officially supported method is using the format. IDML is Adobe’s XML-based, human-readable representation of an InDesign document. Because it is a plain-text standard, it strips away version-specific binary code, making it universally readable by any InDesign version from CS4 onwards.
If you're having trouble converting your file using the above methods, you can try using a third-party plugin or converter. Some popular options include: how to convert indesign file to older version
. To open a file created in a newer version of InDesign in an older version, you must convert it into a compatible format—most commonly InDesign Markup Language (IDML) The Standard Method: Exporting to IDML The most reliable and officially supported method is