To be honest, I don't see much point to change the file extension to xlsx -
what's more, even if you change the extension manually, Microsoft Excel
won't be able to open the file because Microsoft Office
will detect the difference between the MIME
type and the file content and will then add its own autodetected extension.
It would be better to leave the default file extension and then re-save the file in the format you like.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.