The FAQ covers that.
http://xenforo.com/community/threads/resource-manager-faq.46527/
Is it possible to automatically add content from existing forum threads?
No, resources must be added manually.
Can existing threads be converted into resources?
No, resources must be added manually.
Can new resources be linked to existing threads?
Yes, by merging the new resource discussion thread with the existing thread. Or alternatively, use this add-on: http://xenforo.com/community/resources/resource-manager-thread-reassign.1560/
http://xenforo.com/community/threads/resource-manager-faq.46527/
Is it possible to automatically add content from existing forum threads?
No, resources must be added manually.
Can existing threads be converted into resources?
No, resources must be added manually.
Can new resources be linked to existing threads?
Yes, by merging the new resource discussion thread with the existing thread. Or alternatively, use this add-on: http://xenforo.com/community/resources/resource-manager-thread-reassign.1560/