Open Source Document Viewer For Websites: FlexPaper
FlexPaper is an open source document viewer component for displaying PDF files inside websites or Flash applications.
The component does not exactly display PDF files but the PDF-to-SWF converted files in a Acrobat Reader-like interface.
Usage is pretty simple, just inserting the SWF file + customizing the options and there are free tools to convert documents, like SwfTools.
FlexPaper supports zoom in/out, paging, fullscreen, search and printing the documents viewed.
Optionally, it is possible to use the component in Adobe Flex as a SWC source file comes with the download.