After migrating a client for Office 2003 to Office 2010, the problem was that the client had his old files on a .doc (office 2003 format). In order to avoid opening any document and save them under Word 2010 docx format, I found a tool called Microsoft Office Migration Planning Manager and followed this way to convert them on the server.
Download the compatibility pack from here
Download the Microsoft Office Migration Planning Manager here
After that you have to play around with OFC.INI file