Document link in the backend broken

One-sentence description

The document link in the backend is broken.

Current behaviour

When clicking on a link to download a document in the backend, you a re directed to 404 page instead of the document.

Expected behaviour

Either a redirect to the document or no link to the document.

Steps to reproduce

1. Go to the backend page of the bylaws
2. Click on the the link documents/miscellaneous/statuten_xImuGrw.pdf