The Document Processing Library can be also used standalone without the AJAX controls. You can see how in this help article: http://www.telerik.com/help/wpf/radwordsprocessing-overview.html.

Hi guys, 

The requested feature is supported since the Q2 2014 release of the AJAX suite, which now features the Telerik Document Processing library. You can see how to import and export  Word documents in/from RadEditor in this help article: http://www.telerik.com/help/aspnet-ajax/editor-import-export-to-word.html

Best regards,
Rumen

I also have a requirement to open docx file from the server in a web app and make some editing and save it back to the server.

It would be very helpful if the import can import exactly same formatting in Word.
Most of the time our client get the content from Word document and are required 
to follow the formatting. They do not have much time to reformat the content.

Thanks!

Please allow us to import .docx files!  This would be enormously helpful - and save my company!