It is what you use to open themes with.
The Windows common shell DLL is located at
However is not what you use to change themes. To change themes right-click on the desktop and then you will have the ability to change the look and appearance of Windows.
If this is not what your looking for then please post a follow up with more details.
Hope this helps,
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If you have it open in WinRAR, it is probably within a compressed directory. Close WinRAR, navigate to where the directory you just had open is(the icon should be a little pile of purple books) Right-click on it and click “Extract to [name of file]” Then open the newly extracted folder and your file will be in there. Now, to change it’s extension, you need to have file extensions showing, so at the top of the Window, click Organize>Folder And Search Options That will open a window called “Folder Options”. Click the ‘View’ tab. Make sure ‘Hide extensions for known file types’ is unchecked. Then click Apply. Now go back to the file you want to make a dll. Right-click on it and select Rename. Just change it to delete the other extension(ie. .txt) and change it to .dll
Try Open Office: http://www.openoffice.org/