The R1 2020 SP1 release introduces the new ExportAs and Open built-in tools that allow easy import of Excel files and export to Excel or PDF file.
The previous versions can use the Client API of the control for import/export of Excel files.
For Export you can invoke the saveAsExcel() function
on the RadSpreadsheet object and the file will directly prompt you to download in your browser.
As for the Import - you can use the fromFile() passing the actual Excel file to the function. For example, the RadAsyncUpload control
can be used for selection of a file. In the OnClientFileSelected client-side event of the RadAsyncUpload, get a reference to
the selected file and supply the RadSpreadsheet with it:
function OnClientFileSelected(sender,args) {
var file = args.get_fileInputField().files[0]; // get the selected file from the RadAsyncUpload
var spreadsheet = $find("<%= RadSpreadsheet1.ClientID %>");
spreadsheet.fromFile(file); //supply the RadSpreadsheet control with the Excel file.
$(args.get_row()).remove(); //remove the row, visualizing the selection in the RadAsyncUpload
}