Do you want to develop an add-in targeting multiple versions of Office? And you have basic questions like “Is it possible to do? ” and “How to do it?” ? Then you came to the right place. Few months back, I got a requirement to developed add-ins for Outlook 2003 and Outlook 2007. The functionality for both the versions is same. A doubt stroked… when the functionality is same, why would I develop two add-ins separately? Why don’t I make a single build for both the versions of Office?

Then I started searching for techniques to develop add-ins which works in both (2003 and 2007) and read many articles written by VSTO Experts in their blogs, Official VSTO Blog, MSDN, Forums and what not.

Misha Says:

Theoretically, you can develop an add-in for multiple versions of Microsoft Office by catering to the lowest common denominator. This means if you use an Excel 2003 add-in template in Visual Studio 2008, you would be able to develop and debug this with Excel 2007. However if you try this, you may meet these error messages: “You cannot debug or run this project, because the required version of the Microsoft Office application is not installed.”, followed by “Unable to start debugging.”

You can develop Office 2003 add-in in a system where Office 2007 is installed. The following is the procedure that demonstrates how to update your Visual Studio debugging options to use Microsoft Outlook 2007 to debug an add-in targeting Microsoft Outlook 2003.

1. On the Project menu, click on ProjectName Properties
2. Click on the Debug tab
3. In the Start Action pane, click the Start external program radio button
4. Click the file browser button and navigate to %ProgramFiles%\Microsoft Office\Office12
5. Choose Outlook.exe and click Open
6. Press F5 to debug your add-in

For more details. Go through this article in Misha Shneerson’s Blog.

There are some tips and tricks to be followed and the things that one needs to take care while developing add-ins targeting multiple versions of Office in Andrew’s Blog. Have a look at this too. You might find it interesting and useful.

http://blogs.msdn.com/andreww/archive/2007/06/15/can-you-build-one-add-in-for-multiple-versions-of-office.aspx

Here is an MSDN article on Running Solutions in Different Versions of Microsoft Office

http://msdn.microsoft.com/en-us/library/bb772080.aspx

Hope this helps!