pdftotext is a handy little tool to convert pdf files to plain text. It’s part of Fedora’s poppler-utils package and can be installed with yum: You can use pdftotext and the GNU findutils to search for a specific string in multiple pdf documents: See also pdftotext manpage, find manpage, grep manpage
Just a quick one-liner: For the multitude of options (e.g. to flatten the directory structure) have a look at the wget manpage.
Since the functionality has been merged into yum itself, yum presto was discontinued with Fedora 19. To disable the usage of Delta RPMS there is now an additional parameter in /etc/yum.conf