You can limit the types of files that students can upload when they submit an assignment. Leaving this new field blank will continue to allow students to submit any type of file.

In the Adding or Updating an assignment page, the Submission types option area includes a field for indicating what types of files you will accept for this assignment.

To prevent students from uploading anything other than a Word document, for instance, you'd enter .doc and .docx in the field, separated by a comma and space, as shown in this example. (Use the Choose option to select options rather than entering them manually.)

As shown below, the file type limitations are then displayed in the student's submission page. If a student attempts to upload a different file type, the file will not be accepted.