Sorry I’m late to the party everyone.
The opening poster did contact me directly, but can share the following information. This was given to me by one of the InDesign developers some time ago, but not a lot has changed (with the exception of being able to import HEIC and SVG). Their response is as follows:
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I just double checked and found that any file that can be imported (File > Place) into InDesign are supported via Data merge. The image type supported for ID 14.0.2 are:
PNG
PSD
PDD
PCX
BMP
RLE
GIF
SCT
CT
TIF
TIFF
JPG
JPEG
JPE
PCT
We also support and Data Merge is widely used for vectors like:
AI
EPS
PDF
Having said that, please note that some other file types can also be imported into InDesign (hence can also be used in Data Merge). There isn’t an explicit support for them, but they should organically work.
IDMS: IDMS is not an importable file format but rather a group of different items which can be created/placed in InDesign. By this I mean that when an IDMS is bought into InDesign it, it break into its more granular level placing each of the asset which constituted it. Hence what user is seeing is correct and expected.
Text-file: They also are not image formats and hence will not work.
Multi page documents/artworks: Yes only first page gets imported via Data Merge
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HTH
Colin