How do my students move past a pdf file within a module

[nancy_ford]

My students continue to have problems with the student app.  It will not load content, or freeze unexpectedly.  Currently, students are getting stuck in a module that I have a pdf set to view only.  Their next and previous buttons are grayed out and they cannot move forward in the module.  Is this a problem with the app or Canvas as a whole? Is there something I have done wrong in setting this up, or is there something my students are missing?  Thanks for your help!