Trusted Documents provides a simple one click step to always enable active content (e.g. Macros, ActiveX controls etc.) in a document. Trusted Documents remembers the first time you enabled the content and unless the trust record for that document changes, it doesn’t bother you with a security notification for the content anymore. With Trusted Documents, the trust’s recorded per file basis, and is added to Current User section of your local registry and contains file’s full path along with other data such as the created time for a document. Note that because ‘trust records’ are stored on a specific machine you’ll get prompted again if you open the file on another computer. Also since the trust record consists of more than just the file’s path it protects against social engineering attacks such as replacing existing trusted documents with malicious documents that have the same name.
Full Article: Office 2010 blog