How to search for records where a field doesn't exist

If this has been answered in another thread, please link it here. It could be described in different ways by different people and I was not able to think of any unique keywords or phrases that would return relevant answers from the forums.

Does anyone know how to pull up records in a search based on a field not existing? I would like to have a saved search that contains journal citations that don't have a PDF. When I search with "Attachment File Type" is not "PDF", it pulls up everything with at least one attachment that isn't a PDF, which is pretty much everything.

This is an old discussion that has not been active in a long time. Instead of commenting here, you should start a new discussion. If you think the content of this discussion is still relevant, you can link to it from your new discussion.