We made a decision some while back that we would not expose the files uploaded to reference, to the public when guidelines are published. This was because of fear for copyright issues.
We are planning to put in place a feature to allow exposing these files in a safer way, but in the mean time we have a workaround:
You can add the link to the uploaded document in the "Website" element of your reference.
1. Attach a document to your reference
2. Click on the document to open it in a new tab
3. Copy the URL link in the tab that shows the document
4. Open up the edit-form of your reference
5. Paste the link you copied into the "Website" element
6. If you attach the reference to a PICO or a Recommendation, that "Website" link will now be accessible for anyone that reads your guideline.