If I create an IDML-document with my Mac InDesign CS6, can I (or my clients) open it on Windows InDesign CS4? Are there any problems, that may occur?
Yes, there are a lot.
Even if they will be able to open it, the document will change:
Another problems are the fonts. The Mac can read Windows fonts, Windows can't read mac-only fonts. Use OTF at the best.
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