Universal: runs on iPad, iPhone and iPod touch.
Uses Core Data to keep track of PDF documents.
PDF documents can be organized into folders.
Supports iTunes File Sharing for file transfers.
Handles "Open In..." from other apps (Mail, etc).
Multithreaded giving it a responsive UI.
In-App HTML-based help.
iBooks-like document navigation.
Device rotation and all orientations.
Encrypted (password protected) PDFs.
PDF links (URI and go to page).
PDFs with rotated pages.