Gantt charts can be exported as PDF files by selecting "Microsoft print to PDF" or an external PDF application called "CutePDF" as a printer
Once installed CutePDF will appear as a printer in the usual list of printers from which you can pick when you print the map or the Gantt chart. If you select the CutePDF option and click Print you will be given the opportunity to select a filename for your PDF document and a location in which to save it. CutePDF will then create a PDF file of your map or Gantt chart.
CutePDF is available here: http://www.cutepdf.com/products/cutepdf/writer.asp
(Please note that CutePDF is free for non-commercial use. If you intend to use this tool in a commercial environment you will require the paid-for Professional version.)