We do not allow hotlinking (linking to content hosted in other websites or cloud storage) at all. You can simply put attachments to resources, provided it is not copyright protected. If you upload question papers or anything else that are intellectual properties of other persons or institutions, you could lead yourself into legal troubles.
If you need to post questions, it is better to make a resource about it. Post the questions in the body of the article itself. Remember, no search engine can crawl PDF files or other attachments. Your content is readable by search engines only if you make it in the text format. Thus, putting the questions in the body of the article itself will have increased chances of getting traffic and thereby increased chances of earning more revenue.