PDF ++ / Can't Highlight the text

Hello.

When I tried to highligth, copy and paste em PDF while using PDF ++, nothing happens.
I’m using the app on other vaults and works perfectly fine. Only on this particulary one doens’t.
Is that 'cos the PDF was made with a image archive (jpg’s with text)?

Or this is just an set up thing?

Thanks for the answers
Cheers