For better or worse, printed manuals are being replaced by software manuals, mostly pdf. This is true of most Apple Manuals, and is very common among other software vendors. It is for mainly this reason that I bought an iPad. Reading on an iPad is great, and you have a separate screen for documentation. If the document has links in its table of contents, index, and content, it is arguably better than a paper manual.

The iPad does not come with an app for reading pdfs. I have found GoodReader to work great, but others are available.