It's because an IPad or iPhone sometimes has trouble opening a PDF file in a browser.

Download the files to your iPad / iPhone first and then use "open with iBooks."

We have tried this on iPads 1, 2 and 4 and it works OK on both with IOS 7 and IBooks.

If you aren't able to download the files to you iPad email us at and we'll send them as attachments. Then you may open them in iBooks and it should work fine.