In the 'new order form' configuration you have now the possibility to display the field 'reference material', to allow your clients to upload attachments when they place an order.
To make this field visible in a 'new order form' configuration you should first navigate to “Settings > New order form”, select your configuration and go to the “order settings” tab of your option.
Scroll down until “Upload reference material”. There you can make this field required or just visible and add a custom help text to show in the order form.
Just save your configuration and the field is now available in the form:
The files uploaded as reference material are ignored during the word count / estimation but are still listed in step 2:
Finally, the reference material is copied in a specific folder of the order library: