What of InDesign do you currently have access to?

If you see a warning pop-up saying that saving as IDML creates a separate file and the active document will not be saved, don't panic! Simply click "OK" and remember to save your original file separately afterward to preserve your work.

If you don't own InDesign at all and need to convert a file someone sent you, use these browser-based alternatives: 1. Lucidpress (now Marq)

CS3 and older do not support IDML. You must ask the creator to save as INX (InDesign Interchange), which is a nearly extinct format. For free, your only option is to install a virtual machine with an old OS.

If you need to convert a file for use in InDesign CS3 or earlier, IDML won't work—those versions predate the IDML format. In this case, you'll need to use the older format, which was introduced with InDesign CS2.

IDML is a universal InDesign exchange format. It opens in InDesign CS4 and newer .

While not "free," this is a valuable mention for those needing to convert files without installing any software.

If you used a feature in 2026 that did not exist in CS6, that feature will not work in the older version.