I have been trying to open a Word document using C# in VS2010. But I have been successful so far. I have tried searching for answers but all in vain. In the reference sectio
You need to make sure that both Microsoft Office and Visual Studio Tools For Office (VSTO) are installed on the machine.
VSTO is not the solution; Visual Studio 2010 has it built in.
I found the problem for me with the exact same error that you are getting was that I installed Office from the download using the "Click to run". I did download Office the first time I installed. This time I actually used the install DVD and now my code works perfectly. If you don't have the DVD then you can download the trial ISO file instead of the "Click to run" exe.
Word 2010 must be installed on the machine.