What an IDML File Is and Why Design Programs Create Them

An IDML file is a design document that Adobe InDesign creates when you save your work

IDML stands for "InDesign Markup Language." It is the file format that Adobe InDesign uses to store page layouts, text, images, and design elements. When you open InDesign and create a brochure, magazine spread, or poster, then save it, you are creating an IDML file (or an INDD file, which is InDesign's native format). The IDML version exists so that older versions of InDesign and other design programs can open and read the file.

Think of it like this: if you write a document in Microsoft Word and save it as a .docx file, that is Word's native format. If you save the same document as a .txt file, it becomes plain text that almost any program can read. IDML works the same way — it is InDesign's way of making your design readable to programs other than the newest version of InDesign itself.

Key Takeaways

IDML files are created by Adobe InDesign and contain all the design elements, text, and layout information for a page design project.
IDML is a more portable format than InDesign's native INDD format, meaning older versions of InDesign and some other design programs can open it.
You do not need to do anything special to create an IDML file — InDesign can save directly to IDML format from the File menu.
If you receive an IDML file from someone else, you can open it in InDesign, but you may lose some advanced features if your version of InDesign is older than the one used to create it.

When InDesign creates IDML files automatically

InDesign creates IDML files in two situations. First, when you choose to save your document as IDML instead of INDD. Second, when you save an InDesign document in a version older than the one you are currently using — InDesign automatically converts it to IDML so that older software can still open it.

For example, if you are using InDesign 2024 and you save a file as IDML, someone using InDesign 2020 can open that file. If you save it as INDD (the native format), they may not be able to open it at all, or they may lose some of the newer design features you used. This is why IDML exists — it is a bridge between different versions of the same program.

What information an IDML file contains

An IDML file holds everything you put into your InDesign document: the page size and margins, text and fonts, images and graphics, colors and effects, layers, and the exact position of every element on the page. It also stores information about how text flows from one text box to another, which images are linked versus embedded, and any interactive elements like buttons or hyperlinks.

The file itself is actually a compressed folder (similar to a .zip file) that contains XML code — a type of text-based code that describes the design. This is why it is called "markup language." When you open an IDML file in InDesign, the program reads this code and reconstructs your design on screen.

The difference between IDML and INDD files

INDD is InDesign's native format — the format the program prefers to use. INDD files are usually smaller and load faster because they are not converted to XML code. INDD files also preserve every single feature and setting that InDesign supports, including the newest ones.

IDML is the open, portable version. It is larger because it is stored as XML code, and it may not preserve every advanced feature if you are using a very new version of InDesign. However, IDML files can be opened by older versions of InDesign and by some other design programs that support the format. If you are sharing a file with someone who uses an older version of InDesign, or if you want to may support your file can be opened by multiple programs, IDML is the safer choice.

How to save a document as IDML

Open your InDesign document. Go to File, then choose Export. In the dialog that appears, change the file type dropdown to "Adobe InDesign Markup (IDML)." Choose where you want to save the file, give it a name, and click Export. InDesign will create the IDML file in that location.

You can also use File > Save As and choose IDML from the format dropdown, though Export is the more common method. Either way, your original INDD file remains unchanged — you are creating a copy in IDML format.

When you might need to use IDML instead of INDD

Use IDML when you are sharing a file with someone who uses an older version of InDesign. If a colleague is still on InDesign 2021 and you are on InDesign 2024, sending them an IDML file means they can open it without losing your work. Sending them an INDD file might result in an error or missing features.

You might also use IDML if you are archiving a design for long-term storage and want to may support it can be opened years from now, even if InDesign versions change. Some designers also use IDML as a backup format because the XML structure makes it slightly more resistant to file corruption than INDD.

IDML is also useful if you are working with design software other than InDesign. Some programs like Affinity Publisher and Scribus can read IDML files, though they may not preserve every design element perfectly. If you need to move a design from InDesign to another program, IDML is often the best format to try first.

What happens when you open an IDML file

When you open an IDML file in InDesign, the program converts it back from XML code into the design you see on screen. If the IDML file was created in an older version of InDesign than the one you are using, InDesign will ask whether you want to update the file to the current version. If you click yes, the file is converted to INDD format and gains access to newer features.

If you open an IDML file that was created in a newer version of InDesign than the one you have, some features may not display correctly or may be lost. InDesign will usually warn you about this when you open the file. In that case, you may need to ask the person who created the file to save it in an older format, or you may need to upgrade your version of InDesign.

Frequently Asked Questions

Can I open an IDML file without Adobe InDesign?

Some design programs like Affinity Publisher and Scribus can open IDML files, though they may not display every element exactly as it appears in InDesign. If you do not have InDesign and need to view or edit an IDML file, try opening it in one of these programs. However, for full compatibility and to preserve all design features, InDesign is the intended program.

Is IDML the same as PDF?

No. IDML is an editable design file that contains all the layers, text, and elements of your InDesign document. PDF is a fixed format meant for viewing and printing — you cannot edit the design elements in a PDF the way you can in IDML. If you need someone to view your design without editing it, PDF is better. If you need them to edit it, IDML is better.

Why is my IDML file so much larger than my INDD file?

IDML files are stored as XML code, which takes up more space than InDesign's native binary format. The difference is usually not huge, but an IDML file may be 20 to 40 percent larger than the equivalent INDD file. This is normal and not a sign of a problem.

What if someone sends me an IDML file and I cannot open it?

First, make sure you have Adobe InDesign installed — IDML files are designed for InDesign. If you have InDesign but still cannot open the file, the file may be corrupted, or it may have been created in a much newer version of InDesign than you have. Ask the person who created it to resave it in INDD format or in an older IDML version.

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