Is it possible to add customizations to Word 2007 (.docx) file using VSTO2005 SE

Creating a VSTO add-in for Visio 2007
Creating a VSTO add-in project for Visio is really simple. After you download and install the Visual Studio 2005 Tools for the 2007 Office System, you will get several new project templates in Visual Studio. Under your preferred programming language, let’s say Visual Basic, expand Office, and then 2007 Add-ins. There you will find a project template to create a Visio Add-in.

Here are the steps to follow to create your first VSTO add-in for Visio 2007:

1. Start Visual Studio 2005. Click Create Project.

2. Under Visual Basic | Office | 2007 Add-ins, and then select Visio Add-in.

3. Type MyVisioVSTOAddin for the name of the project. Click OK.

Visual Studio will then create a new project for a VSTO add-in that can be loaded in Visio 2007. The project will have all the required references, including the Visio 2007 Primary Interop Assembly. The debug settings of the project will be set so that when you press F5 to debug, Visio starts up. A class named ThisAddIn will also be defined automatically for you. This class replaces the Connect class that you may have been familiar with in a Shared Add-in. Finally, Visual Studio will create a new setup project for your add-in to get you started. (Emphasis on the “to get you started”-- you need to do more to actually get it to deploy your add-in on a test machine.)

ThisAddIn is an improvement from the Connect class. Instead of the four methods you had to implement with IDTExensibility interface, ThisAddIn requires two: Startup and Shutdown. ThisAddIn also takes advantage of the partial class feature introduces with Visual Studio 2005. The VSTO add-in project template adds ThisAddIn.Designer.vb, a partial class that contains generated code to support VSTO add-in functionality. Tip: If you are using Visual Basic, you might need to click the “Show All Files” option under the Project menu to see ThisAddIn.Designer.vb.

By default the partial class defined in ThisAddIn.Designer.vb declares the Visio Application object using WithEvents:

Friend WithEvents Application As Microsoft.Office.Interop.Visio.Application

I strongly recommend that you remove the WithEvents keyword. As you may know, Visio has two event handling models. The first is by using the WithEvents keyword, the second is by using the AddAdvise method. When you use AddAdvise, Visio will raise an event for the events that you specify. When you use WithEvents, Visio will raise all events, even though you may not have an event handlers defined for all events. I recommend that you always use AddAdvise when creating Visio solutions because Visio won’t have to raise events for events you don’t care about.

For now, let’s display a simple “Hello, world!” message box when Visio starts up.

4. Add the following code to the ThisAdd_Startup procedure:

System.Windows.Forms.MessageBox.Show("Hello, world!")

5. Compile and run.

When you run the code, Visio should start up and display “Hello, world!” in a message box.

from:http://blogs.msdn.com/chcast/archive/2007/03/28/creating-visio-add-ins-with-vsto-2005-se.aspx