It is not possible to search words in certain PDF files, e.g. https://arxiv.org/abs/1905.00116 (while e.g. Chromium is able to do it).

local/zathura 0.4.5-1 Minimalistic document viewer local/zathura-pdf-mupdf 0.3.5-2 PDF support for Zathura (MuPDF backend) (Supports PDF, ePub, and OpenXPS)