At present there is an issue affecting Office 2013 document containing text box’s when attempting to view them in Turn It in. Currently anything inside the text box’s will not display in Turn it in so will not be visible to mark. An example of this can be seen below, this is the same page from both documents. This issue has been reported to Turn It in and they are working on a fix.
For now it is possible to down load and view the document complete with the missing items, in the Turn it in preview window were you would normally mark, click the image of the printer in the lower right hand corner and click ‘download submitted file’
If you have office 2010 installed you will have the same issue as describe above but you can install a Microsoft patch which will allow you to view the missing content, this patch can be found here - https://www.microsoft.com/en-us/download/details.aspx?id=38828