New to OS X 10.9 Mavericks is the iBooks app, which can manage and read books in EPUB format, as well as PDF files. You can sync these books to iOS devices via iTunes. I’ve written about some of the problems with iBooks here.
One interesting feature in iBooks is a new PDF service that allows you to create PDF files from any document in OS X and save it directly to your iBooks library. This is easy to invoke. Just press Command-P to print a file, then click on the PDF menu and choose Add PDF to iBooks.
This will save the file in your iBooks library. If you have an iOS device set to sync all books (click on the device, then on the Books tab), this will also sync the PDF file automatically the next time you sync the device. So if you want to save PDFs of articles to read, you could use this to save them directly to iBooks, and sync them to your iPad.