One thing that bothers me is: do we really need, for each button related to a PDF document, a logo which is probably trademarked by the Adobe company?
A quick search for icons related to the "Pdf" term does not leave many doubts:
The red "A" is used as a synonym for PDF... even if it is probably meant to identify the "Acrobat" product by Adobe...
Even the Wikipedia authors – often very picky on this kind of issues &ndahs; couldn't find anything better:
Is there really no graphic artists who can come up with an original icons for this format? PDF is an open standard and deserves a vendor neutral icon!
By the way: I think that Google revealed what inspired that logo!