Autodesk Revit Architecture does not contain default PDF export function, just Printing one. That means, you may export your projects using the File ► Print function and select a PDF printer. That requires to have a virtual PDF printer driver installed.
Another option would be to install tools like RTV Xporter from RTV Tools that offer users several export options, including PDF, DWG, DXF etc.
Updated: December 6, 2016