I can not transfer my ebook to my kobo ereader

I Connect my Kobo ereader via USB to my Windows computer (Windows 10). I Launch Adobe Digital Editions. I Drag the eBook that I want to transfer to the picture of my Kobo ereader  on the left. But a "no entry" symbol appears. I can not transfer my ebook to my kobo ereader . What do  I do wrong ?