In case you are using the RadSpreadProcessing Workbook, document properties are yet not available for that. Here is a feature request, which proposes their implementation. I would suggest you cast your vote for that.
If you are using the Kendo Spreadsheet widget, in the excelExport event, you could configure some of the Workbook document properties, which are available in the Kendo ooxml.Workbook implementation (creator and date).
In case you are using the Telerik UI for ASP.NET AJAX RadSpreadsheet, similarly to Kendo, you could handle the OnClientExcelExport event.
I hope that the above helps. If you have any other questions, please do not hesitate to contact us.