Introduction
When using InDesign, you have got two file formats to choose from: INDD and IDML. The former is a preferred option since it is a binary file that contains its own cache.
Similarly to previews for other file extensions, you are also able to upload images and fonts for InDesign projects in the Project editor → General info → Preview files section.
Guidelines
Here are some tips and restrictions you should be aware of:
INDD files by default do not need to have preview files uploaded since the system draws images from the file cache.
IMPORTANT!
There is a prerequisite to that: one has to make sure that the images in an INDD file are linked, otherwise they will not end up in cache.
Fonts and images have to be in one, zipped folder.
You should check if files are zipped correctly, and their file extension is the same as it was before the zipping process; if, for example, you had “.TIF”, and in a ZIP file it is “.tif”, then the files will not load.
Preview images should be in one of four file formats that XTM allows: JPEG, PNG, SVG, GIF.
There is a UI and API limit to the files' size, which currently amounts to 150 MB.