How can I import PDF files to the "Papers" app?

There are many ways to import your PDFs into Papers for iPad. Obviously the preferred way is if you have a Mac and also use Papers for Mac**. The two apps can wirelessly sync their libraries. But also without a Mac there are plenty of ways. You can upload PDFs directly via iTunes, or you can import PDFs attached to an email from Mail on the iPad. Alternatively, use the Papers bookmarklet to open a webpage you found in Mobile Safari and download the PDF from there. Or you can use the built-in search engines to search for articles and download the PDFs.