The type or namespace name 'ThomsonReuters' could not be found (are you missing a using directive or an assembly reference?)
Do we need to register this DLL anywhere on our Dev Envt Or is there any installer which needs to be run?
Basically you don't need to register RFA.NET DLL. I have create a new web application project and I can add RFA8_NET120_x64.dll as a reference on Visual Studio 2013 and I can also expand the DLL in Object Browser without issue(see attached screen shot).
-Can you open RFA8_NET_120_x64.dll in Object Browser? and What version of target framework you set for this project?
-Can you please share your screen shot when the error occurs?