PDF-4+ is not an online database. It is only available on one computer in the Library.
PDF-4+ is installed on the computer workstation near the Research Advisory Desk (Geisel, West Wing) by the windows. Bring a USB drive to save any PDF cards.
The PDF card will download as an XML document, accompanied by an XSL style sheet called pdfcard. Keep the XSL file in the same folder with the XML document, otherwise the PDF card will not be readable when you open it. If you email the PDF card, include the XSL file as well.
Powder Diffraction File (PDF-4+) contains over 365,000 entries of inorganic diffraction data for crystals and powders, "a comprehensive collection of inorganic materials, produced in a standardized format that can be rapidly searched for unknown phase identification. Extensive data mining is facilitated with our 116 display fields coupled with >60 searches."
Along with searching by elements and other options, you can retrieve a specific record by the PDF card number or the older JCPDS number. You may have to add some zeroes to the card number. For example: JCPDS 27-0689 would be searched as 00-027-0689.
The International Centre for Diffraction Data (ICDD) provides an excellent set of tutorials to help you get the most out of PDF-4+'s searching and data mining capabilities.