Hi Bharath,
Thanks for your interests in Syncfusion products.
For adding new elements to the Document Container while it loads, you could make use of the Loaded event in the Document Container. As a reference we have implemented a simple for you. Kindly download it from the below mentioned location.
http://WebSamples.Syncfusion.com/WPFSupport/Samples/DocumentContainer.zipPlease let us know if you have any queries.
Regards,
Bala.