As per discussion, Appsheet is not capable of opening file:// links (e.g. to pdf documents) on servers that are accessible to all users
Meanwhile http:// links to pdf documents on the web are possible
Access to file://xyz.pdf is a logical extension
A key example is a business process App used by both mobile users and desktop users who have access to a common file-system. There are very few types of App where seamless integration of mobile and desktop is not a given requirement.