Hi Jürgen,
Thank you for your interest in Essential DocIO.
Currently, it is not possible to insert the whole content of an existing document to the current document. I have added this as a feature request with our development team. You can track the live status of this feature here,
Feature Request #1191 - Add a feature for inserting external files to the current document
Please let me know if you have questions.
Thanks,
Prabhu