In old quizzes and new_quizzes it appears that Google Doc Files cannot be uploaded for the file upload question in a quiz. This has also been confirmed in Why can't I select the google doc to upload to a "file upload" question on a quiz? submitted by Shirley Lopez.
Our students, like many other students, are using Chromebooks. Essentially, their "hard drive" is their Google Drive. It would be nice if they would not have to convert their Google Docs to PDFs before submitting them as a file upload quiz question. With the ability to submit Google Docs to online assignment submissions (which are converted to Office Docs in the process), it would also be nice to have the ability to upload Google Docs to the file upload question in Quizzes. It makes sense that this would not be developed in old quizzes, but it would be a great feature to include in new quizzes.