About InDesign

Adobe InDesign is a walled garden—a platform where the provider controls applications and content, and access is restricted. This becomes problematic when you don’t want to do everything within their ecosystem.

This becomes particularly problematic when Adobe decides to cut off access to the accounts of a category of users, thus making it impossible to open one’s files. It also becomes a problem when trying to publish a multi-format document under chosen terms, because extracting content from InDesign is a difficult task.

The different export formats

Exporting documents from InDesign might be enough to reuse content edited in it. However, these exports are not designed for reuse, and each comes with drawbacks.

PDF

If you’re exporting a facsimile of your workspace, InDesign is undoubtedly the best candidate. However, creating an accessible PDF can be time-consuming, and tools like WeasyPrint or Paged.js can produce more accessible documents of better quality with less effort.

HTML (legacy)

If you want to reuse your editorial content from InDesign for building a website, the legacy HTML export might be a good starting point. However, InDesign removes certain information (such as line-end/start spaces, line breaks, etc.). This can lead to completely unresolvable issues, since there is no way to customize this format conversion.

EPUB

Generating an ebook from InDesign is possible, but it requires many steps and produces a file that is difficult to crack open.

For the collection Déborder Bolloré, the Markdown files output by this converter were fed into the Gabarit Abrüpt. This enabled the production of a lightweight, high-quality EPUB, with source code available in the deborderbollore/ebook repository.

The IDML format

IDML is Adobe InDesign’s “open”[1] format—its backward-compatible format (that is, the format most versions of InDesign can read), as opposed to the INDD format, which is specific to each version. By default, packaging an InDesign project generates an IDML file, meaning many projects, even older ones, exist as IDML files. IDML is also a format that can be read and interpreted without launching InDesign, because an IDML file is actually a kind of zipped archive containing a tree structure of XML files.

Other software can also open IDML files, such as Scribus or Affinity Publisher. However, like InDesign, they offer only a very limited range of export formats.

Even though the format is theoretically open, it remains quite complex. Converting it to a simpler, more widely used and supported format requires many steps—which is why this converter is needed.

Beyond this complexity, the fact that InDesign is a WYSIWYG[2] tool that allows direct formatting[3] makes conversion to more ‘structured’ formats extremely difficult.

For all these reasons, this converter works better when certain formatting best practices are applied (see the formatting guide). In general, most of these recommendations are also issued by Adobe for structuring an InDesign file.

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[1]

The IDML format specification has not been maintained (publicly, at least) since 2012. It is included in the InDesign SDK documentation as the InDesign Markup Language (IDML) Cookbook. An Adobe account is required to download it.

[2]

What you see is what you get.

[3]

Direct formatting refers to unstructured formatting—such as identifying a heading simply by making it bold with a larger font, or placing a block on the page (like an image) without anchoring it in the text flow.