Pook, in addition to that, try the free app from Microsoft. In the Apple App store, search for 'Microsoft Remote Desktop'. One might be better than the other at working with RDSS, but right-click is included, usually by a long-press.
FWIW, what RDSS needs is a bit of a visual makeover for tablets - larger buttons, some different navigation options, etc. Not the next update, but maybe later. I am adjusting to using it on my Surface tablet just fine
Ted