If you would like to save PDF files including Gantt Chart images exported from Gantt Chart Library for WPF or Project Management Library for WPF, you can use Aspose.PDF components from Aspose (a third party ISV).
A sample application showing how you can perform this task (including commented C# source code) is available for download and further guidance: Export PDF Document sample.
Note: In order to use the external Aspose.PDF components you need a separate product license that you can purchase from Aspose. However, a 20% price discount applies if you have already purhcased a DlhSoft product usage license: to obtain the discount, please use ASPOSE4DLH promotional code when submitting the Aspose purchase request form. Read this Aspose Company News article for more information.