If you have two different files with different number of fields (for example fileA with {Question, Answer} and fileB with {Chapter, Question, Answer}) you can merge them easily.
First, open the file with least number of fields (fileA), then using the Card Designer add fields (Chapter) to match the second file (fileB). Make sure the order of the fields are the same in both files. You can now import the second file (fileB) using → .