According to the revision history, you just added that tag 14 hours ago. So, that tag isn't yet calculated for you since you haven't had any other questions under it.
Tag scores are heavily cached. They are only updated once a day. Your tag scores should be updating sometime in the next 1 to 2 hours. They usually update sometime around midnight UTC. At that time you should see the
[pdf] tag appear in your profile along with your score.
As usual, have patience. :)