Here is how:

1. share the folder where the file will be posted as public. a read permission is sufficient

2. post the file to that folder

3. click on the folder properties, and in the row corresponding to the share  just created, click on the link in the 'Web' column (it starts with /desknow/directfiles/ )

4. this will open a new window, listing the files in the shared folder. The URL displayed in the browser address bar is a valid HTTP link to access the folder

5. to get the URL of the single file, right click on the 'disk' icon next to it and click on 'Copy shortcut'

You can then paste that address anywhere (ex. an email)