IDML or INDD: what is the difference?

INDD is what InDesign saves as it works. IDML is what it exchanges with other versions and other programs. They hold the same document, and you need each at a different moment.

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Side by side

	INDD	IDML
What it is	InDesign's own binary file	A ZIP of XML files
Use it to	Work on and keep the document	Send it on, or feed it to a translation tool
Opens in an older InDesign	No, not one older than the version that saved it	Yes, that is its purpose
Readable by other programs	Not in practice	Yes: CAT tools, scripts and some layout programs
Written by a converter	No	Yes

Which file at which stage

Stage	File	Why
Working on the layout	INDD	It is what InDesign saves as it works
Handing it to someone on another version	IDML	An INDD does not open in a version older than the one that saved it
Translating in a CAT tool	IDML	Translation tools read its text straight out of the XML
Sending to print or for review	PDF	Neither of the others shows the page without InDesign
Keeping it for later	INDD and IDML both	The INDD is your working copy. The IDML can still be opened if your version changes

Why a converter gives you IDML

INDD is not a format others can write. IDML is plain XML, so a program can write it and you can check it.

We ran the same 233 IDML files through InDesign 2021, 2022, 2024, 2025 and 2026, which is the practical meaning of opening across versions. In this set all 233 opened, with the same number of pages. Your own file can differ, so check it in the Preflight panel before hand-off. Opening is not the same as setting alike, though: right-to-left and Indian text breaks differently on 2021 and 2022.

What to do when you get one

Install the fonts it lists.
Open the IDML in InDesign. It opens as a new untitled document.
Save it as INDD and work in that.
Export IDML again when you need to send it on. Features an older version lacks are lost on the way down.

Going back to an older version

If a colleague on a newer version sends you an INDD you cannot open, ask them to use File > Save a Copy and choose InDesign CS4 or later (IDML), or File > Export with the InDesign Markup format. Expect some reflow, above all on 2021 and 2022, which set right-to-left and Indian text differently, so go through the pages after opening.

What is inside an IDML

Rename a copy to .zip and open it: designmap.xml lists the parts, Spreads holds the pages and frames, Stories holds the text, Resources holds styles, fonts and colours, and MasterSpreads holds the masters. It is why a translation tool can read the text straight out, and why a person can look when something is wrong.

Valid is not the same as good

An IDML can pass InDesign's schema and still go wrong. A file whose parts are named against InDesign's rule is refused whole, and a table row taller than its frame hides the rest of the story with no error. None of that shows in the XML.

So when you judge a converter's IDML, open it in InDesign and look at three things the format does not promise: whether the text is threaded or a frame per line, whether the styles mean anything, and whether the Preflight panel is green. Our own check runs the schema first and real InDesign after it, for this reason.

Questions

Can I open IDML without InDesign?

Other layout programs read it to varying degrees. Scribus shows it only roughly, in our tests without nested tables or pictures in cells. InDesign is the judge.

Can you give me an INDD?

No. Open the IDML and save it as INDD, which takes one step.

Does an IDML hold the fonts and pictures?

Pictures yes: they are embedded in our IDML, taken from the document. Fonts no: you install those.

Try it on a file you would otherwise rebuild

Upload the PDF, the Word file or the scan. Download the copy for InDesign, and the translation too if you ordered one, and open them in your version.