As I don't know your exact purpose, here you have some tools for file management:
If you want to know if a file exists or not:
if filetime('c:\mydata\my.qvd) then
//qvd doesn't exist
You can go further the filetime function to control which file you want to import or not, depending of its creation timestamp.
If you want to have a look in a folder:
FOR Each File in filelist ('.\BUFFER_*.xlsx')
(ooxml, no labels, table is Sheet1);
Maybe your solution needs a combination of all these.
Hope it helps.