Is the Excel 2013 plugin API backwards compatible with Excel 2003-2010?

Question

I would like to know if I develop a addin/plugin for Excel 2013 using vs 2012 and .net 4.0 is compatible for all versions of latest Excel 2013 version to 2003 version.

Answer 1

This type of solution will work so long as

The workstation machine has VSTO 2010 runtime installed.
The workstation has .Net Framework 4.0 framework installed.
The workstation has an version of Office 2007 upwards installed. (2010 VSTO runtime doesn't target 2003).

It will not work against Excel 2003.

notes:
By workstation I'm refering to the end-user (deployment) workstation. Any features you use from the API must be present in ALL versions of Office that you wish to target.
So for instance you can't the sparklines object in your addin, or if you do make sure you put an if statement around the code using If(application.Version > 14.0) so that it never gets called in 2003.
Also remember to embed types in your solution.

Answer 2

Using the "Excel 2010 Add-in" project templates in Visual Studio 2012 and equivalents for other Office applications, the answer is "no". Add-ins created using the "2003" and "2007" templates (created using Visual Studio 2010) will work on Office 2003 and later and Office 2007 and later respectively. Add-ins created using the "2010" (created using Visual Studio 2012) templates will work on Office 2010 and later. These are "VSTO"-style add-ins and are specific to the given version of Office or later.

COM add-ins using IDTExtensibility2 (which can be authored using native or managed code) can target older versions subject to API support in down-level versions of the apps. Visual Studio 2010 provided the "Shared Add-in" template which allowed development of .NET add-ins targeting Office applications using this framework. However, I think this project template type has been removed from Visual Studio 2012. With some hacking, however, I believe that the "Visual Studio Add-in" types can be made to load add-ins inside Office apps since they use the same underlying IDTExtensibility2 and related COM interfaces.