It appears the only way to open files in Salesforce1 is via "Salesforce Files" - previously called, "Chatter Files" which is tightly coupled to Chatter. When creating Chatter files, it seems to piggy back off of Content (ContentVersion) functionality and creates a "preview" link for the file - which is then accessible in Salesforce1. Even if we link to ContentVersion files we've created outside of Chatter, we've not found a way to open them in Salesforce1.
Without Chatter enabled, is there any way to open files on the Salesforce1 platform?