I just determined how to get my pdfs to mail from iBooks. Go to your Settings>iCloud. Look at Advanced and then Mail. Under Allow Sending From, I noticed that I had 2 different accounts, firstname.lastname@example.org and email@example.com. One of them was grayed out. I changed the Email account name (under iCloud Account Information) to the one that was not listed, which opened up the grayed out account (under Allow Sending From) and highlighted the newly un-grayed account. Then I went to my Outbox under iCloud and sent out all of the unsent emails.