I have briefly played with the plugin and found this to happen when the webserver doesn’t have write access to some part of the directory structure.
Unfortunately, I don’t know where DKPDF creates the PDF file before serving it to the user (I don’t think it’s the uploads directory as this usually has R/W access so people can upload images etc).
Hope that helps,
Dave
Found this on the authors’ website that might be useful:
http://wp.dinamiko.com/demos/dkpdf/doc/filters/
Particularly the example adding author after post title in PDF header.
