Neither iPad model comes with a built-in PDF reader, though you can view PDFs in the Mail app. There are a number of excellent 3rd party apps in the App Store for viewing and editing PDFs. Two of best I've used are Rotate Pdf Online and GoodReader.
Rotate PDF Online is free. If you'd rather not have to use an app on your iPad, you can download the Adobe Digital Editions app for free — a great PDF reader by Adobe. You can open many types of PDFs with this option, and it supports all the features that you'd expect in an Adobe PDF app such as searching, viewing and printing. The Newsreader app provides a more full-featured PDF reader.