Hi there. My name is ***** ***** welcome to JustAnswer.com.
What file are you trying to open in Dropbox?
These are the type of files that are supported on dropbox.
If this helps please consider to rate my service. If not, please let me know if you need further assistance.
Thank you for your time.
I am sorry, I just wanted to introduce myself but to also give you a place to start as I need to also know a little more detail on what type of file you are trying to open in dropbox.
If you would like I can chat with you through these posts or I can remotely connect to your mac and you can show me exactly what you are trying to open. Just Answer has a satisfaction guarantee therefore if you are not satisfied I can send a request to customer service for your refund.
Please let me know as I would like to help you with your issue.