Browsers often treat file link access through websites differently. Some browsers require a loaded extension in the browser for the users to open a file as opposed to downloading it. Others will attempt to always open a file.
Generally speaking, if you would like for your audience to attempt to automatically open a document in their browser you should select the Document Properties option: Open links in a new window
To set this option click on the 
Document Properties icon and select 'Open links in a new window' and 'Apply'
