The system does not allow for questions to require an uploaded document or any subsequent action to be taken by the applicant if they select a certain answer to a question. As a workaround, you can build a series of questions in order to separate out the if-then steps.  For example, if an applicant needs to upload a document in response to a Yes answer to a previous question, then you can phrase the following question to read, "If you answered 'Yes' to the previous question, please... upload a document/provide more information."