By default Outlook allows you to preview attachments that you receive from emails. However, to some this might be seen as a security risk or just annoying. We can solve either problem by simply turning off attachment previews for Outlook 2010.
In Outlook 2010, Click the File ribbon and Select Options.
The Outlook Options window should pop-up. Here Click Trust Center tab and then Click the Trust Center Settings… button.
The Trust Center window should open. Click the Attachment Handling tab and then Check the box labeled Turn off Attachment Preview.
Now Outlook should now longer allow preview of any attachments that are received. You can also turn off only specific attachments if you Click the Attachment and Document Previewers… button from the same location in the Trust Center.