Seems like user is trying to right-click hold and drag file in to letter body to insert hyperlink to this file.
Same bug i have. Outlook 2010 x64 on Windows 8.1 x64.
When i am dragging with right-click-hold single file or selection of
files nothing happens.
When i am dragging with right-click-hold single folder or selection
folders or selection of files with at least one folder this menu appears and i can choose Create Hyperlink Here. And all hyperlinks will be inserted in to message.
When Outlook 2010 x64 was installed on Windows 7 x64 this worked for file or files.