Comment by ThomasGlanzmann

Mupdf searches large pdfs much faster. However since I switched to wayland/sway I also use zathura because cut & paste works. Mupdf is an X application but I still use it to search large pdfs. But there is also this plugin but I did not try hard enough to get it running: https://github.com/pwmt/zathura-pdf-mupdf. Under xorg worked cut & paste with mupdf.