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. This requires to have a virtual PDF printer driver installed.
Another option would be to install tools like RTV Xporter from RTV Tools which offer users several export options, including PDF, DWG, DXF etc and will allow you rvt to pdf conversion.