I would like to know if I can upload an excel file with a list of form fields.

If I understand correctly, you want to upload an excel file with form fields and convert it to a web form? If that is so, then you may use the Spread2Jot app to fulfill your requirement. Simply upload the file and select the fields that you would like to use. Here's the link to the app: http://www.jotform.com/spread2jot/ 

Please let us know if you need further assistance.