Originally Posted by Blossom
That's because you use a Calibre Profile that doesn't use the tag system. I believe that Calibre only uses the tag system on the Kindle Profile (Not sure about Kindle Fire profile). So it's really isn't adding the pdoc tag to any of your books because you are using the Kindle DX profile.
I use the Hanlin 5 profile on Calibre and it never adds tags to it either.
But isn't that what the OP is doing? Calibre =>Fire.