Hmmm. What version of osTicket / osTicket Awesome are you using?
FYI I just uploaded and downloaded a bunch of files and opened them successfully using osTicket Awesome v1.11-1.0. I tested using.docx, .doc, .xlsx, .png and .jpg files.
If you would like me to look into this for you I will need you to create a temporary agent account (Admin Panel > Agents > Add New Agent) using info@osticketawesome.com. Be sure to give the account full administrative privileges.