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 > Options.
The Outlook Options window should pop-up. Here Click Trust Center > Trust Center Settings.
The Trust Center window should open. Click Attachment Handling > Turn off Attachment Preview checkbox.
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 Previewer button from the same location in the Trust Center.