Hi Fan,
Thanks for contacting Syncfusion support.
We have checked your reported query and currently “Pdf export for manually scheduled Task” is not support in Gantt. So, we have considered this scenario as feature and logged feature request for that which can be tracked from below link.
As we have already lined up with some major features, we could not start this feature immediately. We will implement this support and include in any our upcoming releases.
Regards
Alagumeena.K