Alberto,
In my previous posting you saw I rename and copy the file to a different folder.
What I actually do is I have a file with ImageNo (Unique key), so the uploaded file is copied to that ImageNo.Ext so when you want to download the file Windows automatically opens the right 'Viewer' thing to open the file, PDFs, JPGs, CSVs, DOCs, XLSs, I have not found a file type that does not work.
I also store the original file name and that is what I display on the Browse. As for when you get to too many files like millions, maybe copy ImageNo's 1-49,999 in subfolder \1, Images 50,000 - 99,999 in subfolder \50,000, etc.
Cheers
Charl