If you have more than one Bentley application installed on your computer that is registered to open DGNs, then in ProjectWise Explorer you need to associate which documents you want to open in which application.

For example, if you have both Bentley View and MicroStation installed, and you want a document to automatically open in Bentley View when you double-click the document or select Document > Open, then you need to change the application that the document is associated to in ProjectWise Explorer. Then later, if you or another user want to change the association back to the original application, or any other, you can.