![](https://lh3.googleusercontent.com/-628KGcn9uNg/WE7DEYlUirI/AAAAAAAAAEk/P5EDDKpePJ4WzGz6HcNTLFhidnQY0CQ7QCLcB/s320/pd.png)
I am a huge fan of very simple logos, so here is another suggestion (very rough sketch): It's a piece of paper (letter or a4) folded in two places. The result resembles both a "p" and "d" as well as an mathematical integral sign (as pandoc "integrates" all document formats into a single type). This would probably look best using two, or maybe three, colors.