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One thing I learned recently that it is not only the textual content that can be copyrighted (i.e. the original work) but also the formatting and presentation.
When someone takes something in the PD, packages it up in a PDF or goes as far as to bind it and slap a © on it all they are protected against is the work _in that format_ someone else can easily come along, take the same PD work and re-package it, change the font, etc. and as long as they do it from an original PD source and not a copyrighted re-package both are perfectly legal.