As Rumen explained in his message, the RadEditor control do not have the power to manipulate the data pasted from Excel.
When content is pasted, the content processed is controlled by the desktop applications i.e., browser and MS Excel in this case.
This matter cannot be handled by somehow configuring an web application.
As the content pasted is upon standards based on the XML logic behind Excel and Word files, they can transfer the content between them successfully. Therefore, I suggest prompting the users to paste Excel content in editable HTML element by firstly processing it first trough the MS Word processor (i.e, paste content from Excel to Word and then in RadEditor). This way the content inserted will be more reliable and suitable for e.g., the RadEditor control.
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