Adding Schematics to a Board

If you have imported a single .brd file you will not see any schematics inside the viewer. EAGLE uses to separate files for this. 

Once you have imported the project using a board file just add the schematics file the same way. Once the file arrives Copper will ask you to choose one or more projects where to add the schematics file. 

Select the project and tap on "Done" to start the import and merge process.

Opening the document after that will also show you the schematics.

ZIP-Files

A faster way of importing a whole project is to zip them and import the zip file. This will only require to do the import once.