Ralph,
Did you look back in the email? Just click the PDF icon again and it should come up. As J.A. mentioned, apps own files on iOS. They do not exist and separate, free-ranging entities as they do on Windows. Lots of apps will let you send files to other apps and once in the other app, they can be found there, but you have to look inside the app for the file. You can send PDFs to iBooks, or to any app that can handle PDFs. One app I use a lot is GoodReader. I tend to keep all PDFs I want to keep in there.