Some PDF files cannot be searched: If you have a scanned file, you need to run OCR first (this is only available in Acrobat, not in the free Reader). If that is not the problem, then is it possible that the file was created by a bad PDF generator that did not add all the information to the file that is required to search it. One way to verify this is by selecting a portion of the text in the PDF and copy&pasting it into e.g. a Word document. Do you see the correct text? If not, then you are dealign with a file that cannot be searched. If you cannot even select a few lines of text, you are dealing with a scanned document that needs to be OCRed.
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com