Hi There, AI Builder asks for 5 documents but only allows to select fields from one document. One document may not have field values and hence it should allow to select fields from multiple documents so that it can either get a value or ignore if it is blank.
Today, you should upload as first document a sample that has all the fields you want to recognize filled with values so that you can define all the fields. Then it is not mandatory that these fields be present in other documents.
We are working on making this more flexible so to not have the need to provide a document will all the fields filled with values.