Rashid, if your question is not related to this thead (how to open a PDF via a link), you might want to post a new thread. This will increase your chances of getting an answer as well as better organize threads in general and therefor help other people looking for answers 🙂
Go to http://forums.arcgis.com/forums/111-ArcGIS-Viewer-for-Flex (if it's related to the Flex Viewer), or http://forums.arcgis.com/forums/18-ArcGIS-API-for-Flex (if it's more of an API question), click the "Post New Thread" link at the top right of the page.