With the file extension IDML, documents of the DTP (Desktop Publishing) solution InDesign are marked in the so-called InDesign Markup Language Format. With InDesign, for example, you can create print templates and layouts for print products such as flyers, catalogs or brochures.
Imdl files are documents (extension indd), which were saved via the export function of InDesign via 'File -> Export'. An imdl file is a ZIP-compressed archive containing various XML files. So besides the designmap.Xml, which specifies the global document settings and the document layout, there are also Graphics.Xml, Fonts.Xml and Styles.Xml.
The IMDL format is designed for sharing between different InDesign versions and was introduced with the CS4 version as a replacement for the INX format, but can not be processed by earlier versions.
Most often resolving problems with opening IDML files is very simple. Just install an appropriate program that supports such files. All of the listed programs support IDML files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of IDML files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate IDML files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Adobe InDesign applications is not on the list, select "Browse" option in order to manually locate the directory where Adobe InDesign has been installed.
Sometimes problems with opening IDML files may not lie with the application itself, but can arise due to other causes, such as: