I recently purchased and downloaded a model in 3D Studio format (native format was .max) for use in Cinema 4D Studio R14 (Mac OS).
The scene renders OK in the Picture Viewer, but appears only partially in the Viewport. For example, the model is of a ruined street with a pile of rubble in the foreground. The Perspective View window shows the rubble in the foreground, but nothing else (other than the standard Viewport grid).
My first thought was that the missing geometry must be on a hidden layer – but I have not been able to find any layers.