What is PDF?
http://en.wikipedia.org/wiki/Portable_Document_Format
Reference:
http://www.adobe.com/devnet/pdf/pdf_reference.html
http://www.pdf-tools.com/public/downloads/whitepapers/whitepaper-pdfprimer.pdf
http://www.adobe.com/devnet/livecycle/articles/lc_pdf_overview_format.pdf
Develop resource:
http://sourceforge.net/projects/pdfcreator/
http://www.pdfforge.org/
free & open-source
http://www.software.ebandwagon.co.uk/MakePDF.html
provide library for visual C++ 6.0
http://www.primopdf.com/ the software is free ,but they charge for develop API