Summary
You can use the Name advanced search syntax to search for documents that are not associated with a template.
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Use the following syntax:
{LF:Name="YourDocumentName", Type=B}
For example, if you want to search for all documents that have not been assigned a template, you would use the following advanced search syntax:
{LF:name="*", Type=B}
More Information
The "Type=B" search will only return documents not associated with a template. If you want to also search for documents that are associated with a template, use "Type=D". For example, if you want to search for all documents whether they are associated with a template or not, you can try using the following advanced search syntax:
{LF:name="*", Type=DB}