Can I use the system's default save/new/etc file icons in WPF?

For Visual Studio 2012, 2013, 2015, 2017, and 2019:

The icons are not in the program folder any more.

You can download the Visual Studio Image Library which contains most of the icons at http://www.microsoft.com/en-us/download/details.aspx?id=35825

From this blog post by Brad Abrams back in 2006:

A customer recently asked me if they can use the standard Microsoft explorer icons in their applications. The answer is yes! In fact Soma blogged about the extended set of Icons we have in VS2005, but basically you can find the VS 2005 Image Library at %vs install path%/common7/ide/vs2005imagelibrary/vs2005imagelibrary.zip. The Windows, Office, and Visual Studio icons that we license for reuse are all contained in there.

Yes it's talking about VS 2005, but the same will apply for VS 2008 and VS 2010. For me (with VS 2008 on a 32 bit machine) the path is:

C:\Program Files\Microsoft Visual Studio 9.0\Common7\VS2008ImageLibrary\1033\VS2008ImageLibrary.zip

I've just installed VS2010 and the path is:

C:\Program Files\Microsoft Visual Studio 10.0\Common7\VS2010ImageLibrary\1033\VS2010ImageLibrary.zip