There is a currently known issue (September 22, 2011) that causes students using Mac computers not to be able to open a PDF file embedded in a course. The workaround to this is to set the PDF to open in a new window. To do this, go to where the PDF is located in your course.
1. Select the drop-down action link.
2. Select Edit.
3. Find the "Open in a New Window" option and select Yes.
4. Click Submit.