Surely you just send them the PDF, which they can open in iBooks, and it'll save itself into the documents section, where they can open it when they like. I've got a bunch of things in iBooks that are PDF documents that open like books, so that I can read it just like a book.
Of course, you could create an iBook, and they can download that and open it at will, but pdf's work ok.
 If they've got iPads, they've got iBooks by default, so having the brochure in iBooks is a more natural place to put it.
I've got a book by Cory Doctorow and Charles Stross that was put up as a freebie, PDF download. It's 150 pages long, and sits in the section along with a Sony service manual, insurance documents, and other random stuff.
Otherwise it's going to be an iBook, which you can give away for free, although, ebooks used to be sold as apps, which sat on the home page, before iBooks was created, but you still have to find a way for the client to get hold of the ebook to download it.
I'm sure there's a work-around, but a PDF that the client/customer can just click on on your web site, and then have the option of reading on the web, or opening in iBooks, which is then automatically saved in iBooks seems like the least complicated way of doing it.