How to write current day in file export Macro

[#1]

Hello I write this macro

function exportexcel()

set obj= ActiveDocument.GetSheetObject("CH32")

obj.ExportEx "C:\ProgramData\QlikTech\Documents\filename.xls", 5

end function

What i want to do is write the filename with current date, something like YYYYMMDD_filename.xls. Any idea for it?

Thank you in Advance,

Alfonso