First question would be, why do you need an Open Office document - this is the format Office uses for its files? It makes no difference. I would also suggest to not use DDE, this is old technology and is limited. What are you trying to achieve by using Excel? I have not found any situation where Excel is the tool for the job. Is it a data transfer, or just for review? As Cynthia has stated, ods excel is currently the only way to create Open Office documents, alternatively you could learn how the files are structured - rename an XLSX file to have the extension .ZIP, then open it and you will see a directory structure with XML snippets in various files etc. Its not and easy format to work with unlike the Open Document format used by LibreOffice or similar. I would clarify first what you want to do as again, Excel is really not the tool for the job.
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