You can't add metadata to an swf. In bridge, you can add metadata to images, videos and music files. You can also use html to add metadata to the page that displays your .swf, that's most likely what you want.
Also, if you're using a lot of text in your .swf, it's often advised that you create a ghost page (or, the newer versions of flash do this for you, adding the text used in the .swf to the .html file as a comment).
General notice: from now on, I would like to ask everyone to put [AS2] or [AS3] (corresponding to the version of actionscript you are using on your project) in front of their post titles when the question is actionscript related! Please help us help you faster. Thank you.