Cannot open illustration just bought in Adobe Stock. Latest release of Illustrator: Error Message: "the file is in an unknown format".
Can you please re-download the .ai files from https://stock.adobe.com/Member/LicenseHistory and check if it works now.
If it is in your CC library, delete the same and re-download it and check.
This has been documented here. Adobe Stock Help | Troubleshoot Adobe Stock
Do let me know how it goes.
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