There is pdfgrep, which does exactly what its name suggests.
pdfgrep -R 'a pattern to search recursively from path' /some/path
I've used it for simple searches and it worked fine.
(There are packages in Debian, Ubuntu and Fedora.)
Since version 1.3.0 pdfgrep supports recursive search. This version is available in Ubuntu since Ubuntu 12.10 (Quantal).
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
