Hi Ricardo,
Thank you for your interest in Syncfusion Products.
Currently Essential DocIO does not provide explicit access to the field codes. For your requirement of replacing the field code by a bookmark, we have created a simple sample. Could you please find the sample from the below link. Try running the sample and let us know if this helps you.
Sample:
F983401975397589.zipPlease let us know if you have any queries.
Regards,
Poornima