The data that drives the apps
Follow the instructions in this How To for iTunes File Sharing: viewtopic.php?f=22&t=5
Okay, thanks. I had previously read that page, and it seemed to suggest that Dropbox was a valid alternative to iTunes, and so I never tried the iTunes interface. I see now that it gives direct access to the files internal to iGigBook, which is very different from what Dropbox gives you. I was able to use that interface to load all the 400 individual PDFs and use the mechanism you outlined to build the single, large PDF (and then quickly clean up the 400 individual files). So that part is now also complete.
I think I may be good now.