The new BIMx for AC 16 allows camera/video options, so not sure which version your using?
Depending on what OS your running just use the normal shortcut to capture screenshots (e.g. F5 for Windows).
No there is no function on BIMx to capture screenshots as far as I know.
An easy way would be to use your computer's built in system for screen shots:
On a mac hold down: command + shift + 3
On a PC click the "Print screen key" which will save the image to your clipboard, you can then paste it into a document.