Web to lead Form

I would like to know if it's possible to transfer a file link to an attachment file from Amazon s3 to Zoho CRM. When I open the link in my browser, I see the file download start. But when I send it to Zoho, nothing shows up in the attachment section. However, I am able to upload files directly from my web form and that works fine. I would also like to know if I can specify the file upload source e.g "From Desktop", "Google Docs", "Attachment URL" etc when I am generating a web to lead form. I think this feature does exist in Zoho creator but I did not see it in the CRM.