Here is a video showing you how to take a document that you created in Microsoft Word or Google Docs and change it into a form that allows for the viewer to type in text fields you place on the form, re-save and email it back to you.
*For those using only Google Docs - Once you have created this form, you can upload it back into Google Docs, but do not convert it over to the Google Document format. If you do that, you lose the feature of filling in the form. Sharing the form in it's original PDF format allows the user to get the PDF form from you and then they download it to be able to fill in the fields. You could also just attach the PDF form to an email and send it out.
Google Docs works great for collaborating, but if you want just one student's answer and work at a time, this allows you to go a paperless route.