When you open an email attachment (for a Microsoft Office application) in Microsoft Outlook 2010, the attachment always opens in Read-Only mode. The following figures demonstrate this behavior with Microsoft Excel and Microsoft Word attachment.
Note This behavior is a bit different with Text files. You can open the .txt file attachment and the window will not say "Read-Only". However, if you try to save the file, you will be unable to save the file back to the message. Instead, the Save As dialog box will appear.
A common source of frustration can occur when you open an attachment in Outlook 2007, change that attachment, and then save the attachment. In this scenario, you find that your edits were not actually saved. The changes that you made were written to the temporary copy of the attachment in the Temporary Internet Files folder, and not actually written back to the attachment in the email message. In an attempt to prevent this to your changes in the future, Outlook 2010 now opens attachments as read-only.
To open an attachment in Outlook 2010 so that it is not read-only, please follow these steps:
Open the email message that has the attachment.
On the Actions control in the Ribbon, click Edit Message. (The screen shot for this step is listed below).
Open the attachment.
This is the same default behavior in Outlook 2007 if you open an attachment from the Reading Pane. However, the same does not apply when you double-click to open a message in a new window. Outlook 2010 makes read-only the default even from a new window.