http://www.bram.us/2007/05/25/office-2007-mime-types-for-iis/ http://technet.microsoft.com/en-us/library/ee309278(v=office.12).aspx up vote 27 down vote accepted Yes, it's just an IIS setting: by default, it will only serve files for which the extension matches a defined MIME type . To allow .docx files to be downloaded, follow the steps from the KB article linked above: Open the IIS Microsoft Management Console (MMC), right-click the local computer name, and then click Properties. Click MIME Types. Click New. In the Extension box, type the file name extension that you want (in this case, .docx). In the MIME Type box, type application/vnd.openxmlformats-officedocument.wordprocessingml.document (thanks to @web developer for pointing out this MIME type, which supercedes the 'application/msword' from my original answer). Apply the new settings. Note that you must restart the World Wide Web Publishing Service or wait for the worker process to recycle for t