Web Designer: problems downloading a file

I try to download a file from a simple file directory on computer using a "Download a file" action, but it does nothing at all. The two mandatory fields in this component are filled like this:

Source: File

Path to source file: format("C:\FTP\{0}", from PWODecisionHistory select prop) (which resolves to a valid path)

What's wrong here? Is there any documentation on this component in Web Designer?