Is it possible to create an Office 2003 VSTO add-in from Visual Studio 2010?

Question

We have existing VS 2008 VSTO add-ins for Word 2003 and Excel 2003. We are unable to upgrade the Office version at this time.

We have just tried to upgrade our solution to VS 2010 and it converts and compiles fine, but when building and running the add-in we receive a message saying that the required version of Office is not installed.

Is there any way of getting around this issue (without upgrading to Office 2007 or 2010) so that we can use VS 2010 to build this add-in?

Answer 1

No, unfortunately it's not possible. VSTO 2010 will not compile solutions designed for Office 2003. It is designed to work with with 2007/2010.

To create solutions for Office 2003 you'll need VSTO 2005 on VS2003 or VSTO 2005 SE / VSTO 2008 on VS2008 (in the case of the later, you can also develop for Office 2007).

Answer 2

No. The Office version is tied to the VSTO version which is tied to the Visual Studio version. Since VSTO 2010 does not support Office 2003, you cannot migrate.

Also, you need to be aware that opening a file extension may open the incorrect Office version. For example, on startup the later versions of Office will register themselves into the registry. If you are developing an Excel 2003 VSTO project, but you manually open an Excel 2007 workbook, then 2007 becomes the default. The next time you work on the Excel 2003 VSTO project, it will use Excel 2007. To get back to Excel 2003, you must run excel /regserver.

• Description of the startup switches for Excel at http://support.microsoft.com/kb/291288.