They are vestigial remains of the curved braces in this idea: ┋}▭{┋. (Look at the negative space to see it.) They make more sense in the first idea, but I kept them in the second one because they help the "documents" occupy more horizontal space without making them look out of proportion, and because they form a kind of serifs. But yes, they do make the PD harder to see.
 

Removing the curved outsides might just clean up the design enough that such arrows don't hurt. Give it a go!