Wish there were a way to find only PDFs that haven’t yet been OCR’d. (So I could OCR 'em.) Sorry if I’m “duh” on this. I’ve made several searches in the forum and haven’t found a solution.
I don’t know if this is 100% perfect, but I just did an advanced search / smart group where the kind of document is PDF/PS and the wordcount = 0 and it found a bunch of non-OCRd PDFs for me. So that should get you started 
[size=85]edit: suggestion deleted in favor of Christian’s solution (below) that actually works! 
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Or just use Data > New from Template > Smart Groups > PDFs (not searchable) 
AHH! Yes! Thanks!!! 
While this trick works, it really would be much easier if there was a “PDF+text” option under “kind” when creating smart groups. Could we get this added?
Welcome @Luhmann
The request is noted but PDF Document and PDF+Text are not separate file types. They are both PDFs and the dropdown displays broad types. For example Plain Text will display more than just .txt files.