What Is an IDML File? A Plain-English Guide for Publisher Users

If you've been looking into converting your Microsoft Publisher files, you've probably seen the term IDML. Here's what it actually means, what software opens it, and why it's the best format for preserving editable Publisher layouts.

What IDML stands for

IDML stands for InDesign Markup Language. It's a file format originally developed by Adobe for Adobe InDesign, but it's now an open format supported by several applications. Unlike proprietary formats, IDML is essentially a ZIP archive containing XML files that describe the layout — pages, text frames, image placeholders, colours, and styles.

Because it's open and well-documented, other applications have been able to add full IDML support — most notably Affinity Publisher 2.

What software opens IDML files

For most Publisher users, Affinity Publisher 2 is the natural next step — it's a one-time purchase, runs on Mac and Windows, and opens IDML files directly via File → Open.

Why IDML is better than exporting to Word

When people first try to convert Publisher files, they often look for a Word (.docx) export. The problem: Word is a word processor, not a layout application. When you convert a Publisher file to Word:

• Text frames get merged or repositioned
• Multi-column layouts collapse
• Precise positioning of images and text boxes is lost
• Fonts that don't have a Word equivalent are substituted

IDML preserves the layout as a layout — text frames stay in place, columns are respected, and the visual structure of the original document is maintained. If you ever need to print, update, or re-use the document, IDML gives you something you can actually work with.

Why Publisher doesn't export IDML natively

Publisher has no built-in IDML export. The format is associated with Adobe InDesign, and Microsoft had no business reason to support it. Publisher can export PDF and several image formats, but not IDML.

Getting IDML from a .pub file requires opening it in Publisher and using third-party automation or a conversion service to produce the IDML output. That's exactly what Publisher Conversion does — it runs Publisher on a dedicated machine and produces both a PDF and an IDML file for each .pub you upload.

How to open an IDML file in Affinity Publisher 2

1. Open Affinity Publisher 2
2. File → Open → select the .idml file — it imports directly
3. Right-click the pasteboard (the grey area around the page) and set the color to white — this makes pasteboard content visible
4. Go to View and disable Clip to Canvas — objects outside the page boundary will now appear
5. If prompted about missing fonts, install them or accept substitutions

Most Publisher files open cleanly. Complex files with heavy use of Publisher-specific features (certain text effects, linked text boxes across many pages) may need minor cleanup, but the overall layout comes through faithfully.

What about the .indd format?

.indd is InDesign's native binary format and is not the same as IDML. It's proprietary and version-specific — an .indd file saved in InDesign 2024 may not open in InDesign 2020. IDML is the portable, application-agnostic version of an InDesign document, which is why it's the right format for interchange and migration.