Using this option it is possible to upload files, for example an entry form. One uploaded, put your right mouse button on the link in the name column and select "copy link" or "copy link location". To create a link to it, you then need to go into the Edit tab for the congress and put in an html tag containing the link you just copied. You can use control + V to copy in the link location you copied.

Note this is not very easy to use. At some future date I might add in an easy was to upload an entry form (for ECF congresses you might find it easier to upload your entry form to the ECF calendar and then put a link in to the one there)