What is the difference between IDML and INDD?

INDD is InDesign's native binary document format, tied to specific versions. IDML is an open, XML-based interchange format that is more portable across versions and can be generated programmatically. Both open as editable InDesign layouts.

Explainer

What is IDML, and how is it different from a PDF?

Q: What does IDML stand for?

IDML stands for InDesign Markup Language. It is an open, XML-based interchange format for Adobe InDesign documents, stored as a zipped package of XML files describing the layout, text, styles and objects.

Q: Can Adobe InDesign open an IDML file?

Yes. InDesign opens an .idml file directly (File, Open) and creates a fully editable, untitled document from it. Affinity Publisher can also open IDML files.

Q: Is an IDML file editable?

Yes. Unlike a PDF, which is a flattened final-form file, an IDML describes the layout as structured, editable elements: text frames, named styles, and objects you can move, restyle and reflow.

Last updated June 2026 · by Kelly Fraser, maker of idmly

IDML is InDesign Markup Language: an open, XML-based, fully editable format for Adobe InDesign layouts. An .idml file is a zipped package of XML that describes a document's text frames, named styles, colours and objects, everything InDesign needs to rebuild the layout as a live, editable document.

That's the opposite of a PDF, which is a flattened, final-form file built to look identical everywhere, not to be edited.

If you've ever received an .idml and weren't sure what it was, here's the short, useful version, and why it's the format idmly produces instead of a PDF.

What's inside an IDML file

An IDML is really a ZIP archive of XML documents. Rename one to .zip and you'll find the spreads, stories (the text), styles, and resources laid out as structured data. Because it's XML, it can be read, written and generated by software, not just by InDesign itself. That's exactly how idmly builds one: it writes valid IDML directly from your rendered HTML layout.

IDML vs PDF

IDML vs PDF
	IDML	PDF
Purpose	Editable layout interchange	Fixed final-form display
Text	Live, in named styles	Flattened, often outlined
Editable in InDesign	Fully	No, placed as one graphic
Under the hood	Zipped XML	Flattened page description

IDML vs INDD

.indd is InDesign's native, binary document format, and it's tied to specific InDesign versions, so a newer file won't open in an older InDesign. .idml is the open, portable interchange format: more version-flexible, and generatable by software. When you open an IDML, InDesign creates a fresh untitled document you then save as INDD. Affinity Publisher can open IDML too.

Why it matters for your work

If you want a design you can keep working in, reflow text, swap a font, recolour a chart, you want IDML, not a placed PDF. That's the entire reason idmly outputs a native .idml: so what you get back is a real document, not a picture of one.

Frequently asked questions

What does IDML stand for?

InDesign Markup Language. It's an open, XML-based interchange format for Adobe InDesign documents, stored as a zipped package of XML describing the layout, text, styles and objects.

Can InDesign open an IDML file?

Yes. InDesign opens an .idml directly (File, Open) and creates a fully editable, untitled document. Affinity Publisher can open IDML too.

What's the difference between IDML and INDD?

INDD is InDesign's native binary format, tied to versions. IDML is the open, XML-based interchange format: more portable and generatable by software. Both open as editable layouts.

Is an IDML file editable?

Yes. Unlike a flattened PDF, an IDML describes the layout as structured, editable elements: text frames, named styles, and objects you can move, restyle and reflow.

Want a real .idml from your design?

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