For each category in the app, you can configure which documents can be added.
Navigate to Configuration
Click on Documents in the header
Click on the category you like to edit on the right side.
You can filter in the header to only see the document types that are attached to a certain object (Order, Trip, Invoice, Resource or Product) or to only see the active objects.
Once the document types are enabled in the Available document types section, you can configure them for the customer portal. You will see that you can make a document type both available for viewing and for uploading.
View: your customer can view a document and download it.
Upload: your customer can upload a document.
Once configured, you can add documents in that category. For instance, you can add documents to the consignment (trip) in the individual order page based on the documents that are configured in Trip in Configuration.