We require all students to be able to create and submit ".docx" files so that our instructors and teaching assistants can open and grade student assignments. 

A ".docx" file is a Microsoft Word file type, and the most recent versions of Microsoft Word can create this file type (beginning with 2007).  If you are using an older version of Microsoft Word that does create this file type, you can download a Compatibility Pack from Microsoft.

Alternatively, there are a handful of free web applications that allow you to create and save files with a ".docx" extension:  Google Docs, Word Online, and Zoho Docs.