How to seek for keywords in pdf files

[Xaleandr]

Hello,
I have a problem with KFind application from KDE.
I am trying to seek for all " *.pdf " files in the folder containing a given keyword, but somewhy I can't. I tried to check "Include binary files", but somewhy this solves the problem only partially (some files are found whereas others aren't). On the other hand, I checked manually that (1) There are files which contain the keyword (2) All the files contain text (not "text as image") (3) Both Acroread and KPDF are able to look for the keyword when any of the files is open.

How is it possible to make the search ?
Thanks in advance,
Xaleandr

[apoorv_khurasia]

Since pdf stores the data in it as a pixel map (think in terms of images) you cannot use default UNIX commands such as find or grep to search for regular expressions in it. Any program that aims to do so must include a call to open that file and parse the pixmap data as ASCII chars. KPDF, Acroread and evince etc... do precisely this and so do all applications like Windows Desktop Search/Google Desktop (for MS Windows).