When using Document Manager with Microsoft Word to merge documents, you may encounter the following message:
An error occurred while opening the document. The message returned was: The openDataSource method or property is not available because this command is not available for reading.
Microsoft Word OpenDataSource method is called as part of a Mail Merge operation.
The error may occur when attempting to edit or create a Mail Merge document, or if a document is saved in Microsoft Word in reading mode. When in reading mode, the software is not allowed to call a method (perform a task) on the document, which results in the error message.
Open any Microsoft Office Word file on your computer (ideally one of your mail merge templates).
Click File.
Click Options or Word Options.
Click General.
Untick the box for "Open e-mail attachments and other un-editable files in reading view".
Click Ok.
Close the document.
Open the template that was giving the error message and perform the merge.