Comment 1 for bug 2065501

Did you try disabling the "Advanced search dock" on the "Interface" tab of the settings dialog which should already disable some of that overhead (not sure whether it already actually existed in 0.4.18 though).

Other than that, searching for all occurrences on a page is significantly faster in almost all documents due to the relatively high overhead the underlying libraries have for turning a given page into text. In current versions, all of this happens in the background and optionally in parallel which further reduces the time until results are ready. We even started out with the simpler implementation which tracks only a single current result and it was significantly more janky as searching for the next occurrence on a page is basically as fast/slow as searching for all occurrences on page with Poppler.

So in summary, while it may not be ideal for 3000+ page documents, I think this is still the best compromise given the libraries this program depends on.