Warning message while opening downloaded excel output document.

Summary:

We have a requirement to generate output document in excel format. We able to do that. But when open the generated document as it is in .xls format user gets warning message :

File format and extension of ****.xls do not match. The file could be corrupted or unsafe. Unless you trust its source location dont open it. Do you want to open it anyway?
Is there any way to avoid this warning to the users, as currently we don't have option to download/generate output document in .xlsx format.

Content (please ensure you mask any confidential information):

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