When attempting to mail merge a document, the following error may occur.
To resolve:
Open the document and ensure there are mail merge fields within the document.
See the below knowledge article on creating mail merge documents:
Note: Windows version 10 is a minimum requirement for this functionality to work.
Follow the instructions below to check your Windows version.
Select the Start Windows logo button then select Settings.
In Settings, select System then About.
Check the Windows Specifications - Edition.