I want to search all files which have the same filename, but different extensions.
For example, if there is "source.txt" and "source.pdf", then I want to delete "source.txt". BUT if there is no "source.pdf", then the .txt should stay! (That is why I cannot just delete all .txt files). To complicate matters more, there might be different extensions (e.g. .rtf).
As I wrote, I want to search for such files, not select them. That is what I mean by "Find duplicate files (but without extensions)".
In other words, if there were such an option, I would I select "Find duplicate files", then "Comparison method: filename only" but "Without extension".
What can't you do with a selection that you can do with search results? You could always add the selected files to a collection which will give you the same thing.
If the only issue is that you need to search into sub-folders then Flat Mode should solve that problem.
The duplicate files find should give me the names of the files which are duplicated. I do not know what files have duplicate names beforehand, right? That is the whole point of the search.
I want to search the whole folder structure with (presumably many) files which have duplicate names, but different extensions.
Is this something you'll need to do often or just a one-off?
If it's just a one-off then PM me the list of files and I'll generate the list of duplicates for you. It'd be pretty easy to generate via Excel or a quick program (depending on the size of the list).