How to search for a missing year (nnnn) in filenames?

[EveryThinger]

Is it possible to search for filenames that do not include a four-digit year?

I have several hundred PDF files in a specific path (and its subfolders).
Now I have to find the ones that don't have \d{4} in the file name.

How can I do that?
(It doesn't matter whether a regular expression is necessary or not.)

[void]

!regex:\d{4}

! = NOT

[EveryThinger]

It works perfectly!
Thank you very much for your prompt response.