Preview application is not showing search results when I do Cmd + F to search a string Actually this error occurred after I updated my os to Mojave. Earlier it was working fine. I'm using a MacBook Pro 2015 model.

Caveats -: 

I am searching in pdf files containing texts. 

I've tried the solutions provided over internet, like closing and opening it again. 

Searching works fine when I open the same file in Adobe Reader.
there are multiple type of pdf encodings, some of which disable text selection and thus searching strings, which under the hood selects text and highlights text, is disabled.

check by double clicking on any word. 

1.) if the whole page becomes blue, that means you can't do searching on that page. 

2.) if the word is selected, and still you're unable to search, do comment with details, 

I'll be happy to help!