I have a folder with ~1200 pdf files. In that directory tried a search for a particular word using Dopus-10's search feature and got 25 hits. If I make the search with my desktop search program (Copernic DTS) I get 453 hits. I have verified that Copernic is in fact finding files with the search term that Dopus is not finding.
Although Google DTS can work within Dopus, Copernic can't. However, I don't like Google DTS and have abandoned it. It would be wonderful if Dopus could be fixed to more thoroughly search PDF files that are searchable. (I understand that some PDFs are image-only and are not searchable, but that is not the problem here.)
This has been a long-standing problem in prior Dopus versions. Even though DTS gives fast results, sometimes I need the slower file-by-file search method Dopus uses, so I can employ Dopus' great flexibility in sorting the search results (where Copernic is weak).
In any case, it seems that Dopus should be improved to do thorough PDF searches.