Hi Rolf,
Thank you for using Syncfusion Products.
Currently we do not have support for parsing Drawing tools (Shape Objects), hence we cannot retrieve merge fields present in Shape objects. As an alternative to shape object, please use ordinary textbox to hold merge fields.
We have created a sample application to illustrate on how to use textbox with merge field and retrieve all Merge Field names present in a template document.
Please do find the sample from the attachment and let us know if this helps you.
Regards
Gunasekaran
MailMerge_b8c9df5d.zip