The app you have sounds like it is an app that converts to PDF - whereas ... irb exports the PDF, so it might not list (since it is already a PDF. Would this be correct? if you have iBooks it should import ok. Also other apps that import PDF should list in the Open with ... window (if they coded it to do this.)
I use my computer to compile my single PDF pages into one document as I find it quite quick to do this and organize the order etc.
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