Altium: unable to import from schematic
The problem is that your documents are listed under "Free Documents", meaning they have not been added to a project. In order to fix this, go to File --> New --> Project, select PCB project and give it a name/location.




Once your project is created, right-click it in the projects panel, select "Add existing to project". 



Then add your schematic and PCB files to it. 
Once you do that, you should be able to import changes from the schematic into the PCB.