Hi Tomas,
Thanks for contacting Syncfusion Support,
We have checked the reported query “ how I can add a control, such as a SFDiagram, within a ContentControl of the DockingManager whose DockState is Document, using C# ” from our end. We have added the Diagram control to the ContentControl of the Docking Manager, prepared a simple sample as per your requirement.Please check the sample for your reference.
Please let us know if you have any other concerns we will be glad to assist you.
Regards,
Bharathi R