I'm curious to know whether the PDFKit framework is available for use within the iPhone OS, in order to build a PDF reader a bit more sophisticated than the one available by simply opening PDF documents with UIWebView.
Just wondering if this is an option or not.
The PDFKit is not available on iPhone at this time. Certainly the functionality is there, but Apple has not opened it up in an available framework. You should file a bug on this if you'd like to see it in the future.
If you want more control over PDF, there are many ways to manipulate PDF content using Quartz graphics.
Grab the official sample code called QuartzDemo which has an example on how to manipulate a PDF file using Quartz graphics. The output seems faster than the UIWebView.