Generally, it is sufficient to provide the project organiser with an electronic/digital document when BOTH of the following is true:
1) you have received your invoice/ticket/boarding pass via email;
2) you don’t need to print it to travel.
If you have such documents, you don’t need to print them out, just send them over to the organiser (in one e-mail, preferably).
Original/printed document is needed if:
1) you have received your ticket/receipt/boarding pass in a paper form (e.g. machine printed it out);
2) your electronic ticket/boarding pass is invalid for boarding.