SOLVED! Posting anyway in case it helps someone else.

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Hello Community,

My client sent me an IDML file created on a Mac with the latest version of InDesign (something from 2025).

After checking the box to "Process unsupported versions" I was able to translate it in SDL Trados Studio 2024 18.0.2.3255 on a PC.

I then clicked on "Generate target translations" and Studio produced an IDML target file.

I sent it to the client and they "can't open it" either with "the current version of InDesign or the previous one" (they did not specify the version numbers). They didn't tell me what error message they received or what happened.

I have started a free trial of Adobe InDesign to see if I can figure it out. When I try to open the file myself, I get the message "Cannot open the document C:\Users\etc. Not well-formed"

Update: I searched online for this "not well-formed" InDesign error message and I found in this very forum that the problem might be the comments I added to the translation in Trados. I deleted the comments and tried to open the target file again in InDesign. It worked!