Students using Mac computers might save documents in the Pages format, not in the Word format.  Documents in the Pages format aren't automatically viewable on most PCs.

1) How to prevent students from uploading Pages files.

Edit the assignment. In the Submission Type, restrict upload file types to doc,docx,pdf as in the picture. If a student tries to upload a different type, such as a Pages file, Canvas won't allow it.  (Note: doc, docx, and pdf are the 3 files types that the Canvas speedgrader's commenting system can handle.)

2) How to view Pages files on a PC

There are several ways to view a Pages file on a PC.

  1. Go to  Upload the Pages file. Pick convert to docx. Zamzar will convert in a minute or 2 and email you a link to the result.
  2. Go to  Get an account. (It's free.) Use the online version of Pages to view the pages file.
  3. Rename the pages file to ".zip".  Use a zip viewer to see its contents.  There will likely be a preview.jpg image of the first page of the document.
  4. Put the file on your Google drive. Right-click and choose Open With... Cloud Convert.  Follow the directions to convert to Word format.
  5. Ask the student to convert from Pages to docx.  (Open the pages file. In the “File” menu and choose “Export To”, then select “Word” from the submenu list.)