In the current Surface lexicon, "Surface RT" identifies tablets that run Microsoft's mobile operating system only. That system is a "lite" one and runs only a limited-feature version of Office that does not support TheFormTool.
"Surface Pro," on the other hand, runs the full-feature version of Windows, which supports the full-feature version of Word, which supports TheFormTool.
So, for TheFormTool on the move, choose Surface Pro and make certain to load onto it the full version of Office.