Manually attaching a DataSource when merge fields are not merging but a datasource is created
You can only manually merge to the DOCX datasource not the XML datasource. The XML datasource files are used for automated mail-merges which is currently your issue.
This means the Output as Merged Document option needs to be unticked otherwise the DOCX datasource is automatically cleaned up and deleted when the document production wizard is finished.
1. Run the document production wizard again and deselect Output as Merged Document, so that this step can be manually completed later. Click next and finish the wizard.
This will create 2 datasource files, an XML version which will be used if an Insol function is used to merge the documents and a DOCX version that can be used to manually merge the documents. These files will be saved in the Datasource file.
NB: The datasource file is a hidden file. To show the hidden file click on View > Show Hidden Items. You may also need to change the file type being displayed to All Files (bottom right of page). The file will be an xml file
2. Now open the document to be merged from Document Management and choose Select Recipients>Use an Existing List from the mailings section where highlighted below
3. Choose the DOCX datasource that was created by the document production wizard and click open.
4. When back at the word document click Mailings. Then select Finish and Merge>Edit individual Documents, and select All records
5. This should open a new word document that's populated with the data from the datasource.