What is the IDML file format?
Files with the .idml extension are created with Adobe InDesign, and the full name of the format is the InDesign Markup Language. The application is designed for creating complex graphic layouts of pages, used in magazines, newspapers, brochures, leaflets, books, and eBooks. An .idml file stores arrangement properties, metadata, multimedia elements, text content, formatting, and other layout-specific information.
.idml is the successor of the .inx interchange format, which was harder to edit using third-party software. Adobe redesigned the exchange format to make modifying and creating page layouts more accessible to applications beyond InDesign itself - including tools like Affinity Publisher, QuarkXPress, and Scribus.
.idml is based on XML and packaged as a standard ZIP archive, sharing the same container convention as EPUB and ODF documents. The file begins with the magic bytes 50 4B 03 04 (PK) and stores an uncompressed mimetype entry - application/vnd.adobe.indesign-idml-package - as its first file. Renaming .idml to .zip lets you inspect all internal XML directly.
The root document inside the package is designmap.xml, which links together the following folders:
META-INF/- container descriptorResources/- fonts, colors, and graphic stylesStories/- individual text threadsSpreads/- page spread layoutsMasterSpreads/- master page definitionsXML/- XML tags and attributes for structured content
Security & safety
RISK: LOWAn IDML is XML-in-a-ZIP layout data, not executable, so opening one is safe. Standard archive caution applies to any ZIP from an untrusted source, but there is no active content. The realistic 'risk' is fidelity, not security: non-Adobe importers (Scribus, QuarkXPress) may not reproduce every InDesign feature exactly.
Format details
in a nutshellPrograms that open IDML files
Windows4 apps
Adobe InDesign
Paid File → Open the .idml; InDesign converts it to an untitled document you then save as .indd. The native, full-fidelity editor. 
QuarkXPress
Paid Imports IDML to migrate InDesign layouts into Quark; trial available. Some manual cleanup expected. 
Scribus
Open-source Free DTP app - File → Import → Get Text/Import IDML; opens many IDML files with some loss of styling. Best free fallback. 
Affinity Publisher
Paid File → Open / Place the .idml - best non-Adobe IDML importer; free since the Canva acquisition (2025). Expect minor layout adjustments. 
macOS3 apps
Linux1 app
Scribus
Open-source The practical Linux option - import the .idml (partial fidelity) to view and edit. Technical details
deep spec| Container format | ZIP archive; magic bytes 50 4B 03 04 ("PK" signature at offset 0) |
| Payload encoding | UTF-8 XML across all internal component files |
| MIME type | application/vnd.adobe.indesign-idml-package |
| First ZIP entry | Uncompressed "mimetype" file - same convention used by EPUB and ODF packages |
| Root document | designmap.xml - package manifest that references all component folders |
| Replaced format | .inx (InDesign Interchange), deprecated from InDesign CS4 onward |
| Developer | Adobe Inc. |
| Stories folder | Each text thread stored as a separate Story_*.xml file, allowing independent content editing |
| Spreads folder | Per-spread XML files defining page geometry, object placement, and frame coordinates |
| MasterSpreads folder | Master page definitions applied globally across document pages |
| XML folder | XML tag and attribute definitions for structured/tagged document workflows |
| Resources folder | Document-wide assets: fonts, color swatches, paragraph styles, and character styles |
| Third-party support | Readable and writable by Affinity Publisher, QuarkXPress, and Scribus |
| Interoperability purpose | Designed for cross-application exchange of InDesign layouts without round-trip data loss |
| Inspection method | Rename .idml to .zip to browse and edit all internal XML with any text editor |
| Released | 2008 (InDesign CS4) - replaced the older INX interchange format |
| Open standard | Yes · royalty-free |
| Specification | www.adobe.com |
IDML conversions
Community Q&A
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