Surely you can open 2D drawing easily via file open in the program.

But you also have quick access in the Detailcenter by marking an object
in the list and using the context menu - Open 2D-drawing

If a 2D drawing exists can be seen by the color of the object in detail center:
Grey - nothing available
Green - a 2D drawing is available
Red - a 2D drawing is availabel but not up to date (changes have been made in the model)

To get back to the model, the fastest is by using the green arrow buttons on the lower left hand side.

If you need to know there the 2D drawings for this model are saved this info is alos available.