Out of the box neither WSS 3 nor MOSS 2007 will index content located in Acrobat PDF files, so you need to set up the IFilter.  I’ve also found that that PDF files loaded prior to the installation of the filter won’t be re-crawled automatically, so to be on the safe side you might want to kick off a full crawl.

Here is what I’ve found works for WSS 3.0:

1. First, you need to download the Adobe PDF IFilter 6.0, which you can find at this URL.  You should also get hold of a suitable Icon to use with PDFs, so that when they are listed in a document library they are easily recognisable.  There is a 17 x 17 one available on the Adobe web site here.
2. Once you’ve downloaded the IFilter, install it on your WSS 3.0 server, and then follow the instructions on registry settings in Microsoft KB Article 927675.  I’ve always found that providing the Adobe IFilter installed properly, the only setting I need to add is the Search Extensions one listed in step 2.  Also note step 5 re stopping and re-starting the search service.
3. Now you need to set up the Icon file.  If you downloaded the icon file in step 1 above, you will have a file called pdficon_small.gif.  You need to copy this onto your WSS 3.0 server, into drive:Program FilesCommon FIlesMicrosoft SharedWeb Server extensions12TEMPLATEIMAGES.
4. Next you need to edit the XML file which WSS uses to link file extensions to icons.  This file is called DOCICON.XML and is located at drive:Program FilesCommon FIlesMicrosoft SharedWeb Server extensions12TEMPLATEXML.  Navigate to that folder and locate the file.  I would suggest making a backup copy first, then opening the file in NotePad.  You need to add a mapping key for PDFs at the bottom of the file, above the </ByExtension> closing tag.  The new key will be <Mapping Key=”pdf” Value=”pdficon_small.gif” OpenControl=”"/>  (note that XML is case sensitive so make sure you use same case as previous entries).  Then save the file.
5. That’s pretty much it, but if you already have PDFs uploaded to your WSS server I would recommend starting a full crawl.  You can do the with STSAdm, the command syntax is Stsadm -o spsearch -action fullcrawlstart .  More on this on TechNet here.