How to submit documents

I just saw piles of thrown away folders and other materials in which people send their documents for the Commission. Every letter before arriving at the person in question is going through the postal service, where EVERYTHING is thrown away - all the folders, paper clips, what is left is just papers.
I know every session people are wondering how to send the documents so the reply is easy - as described in the rules of the traineeship - just numbered pages put in the envelope, then there is an internal system of storage so no worries, nothing will be lost. If there however are some small papers you can just stick them on an A4 blank page so that they don't get lost somewhere in the process!

Thank you. I was just wondering if it is a good idea to put all the documents in a folder or just put them in an envelope.