Help with Acrobat FDF support

I just found the very cool looking new FDF functions to support Acrobat forms. According to the documentation at www.php.net I have to download & install the FDF SDK. Found the latest SDK and I put two files from the C directory of the SDK at: /usr/lib/php4/libfdftk.so /usr/include/fdftk.h Then I figured that I had to put something into php.ini to load the FDF code, so I added a line like this to php.ini: extension=libfdftk.so Unfortunately, it doesn't work. I get an error message: Invalid library (maybe not a PHP library) 'libfdftk.so' I've looked all over various newsgroups, forums, etc and that's where the instructions stop, but there must be more to it. Can anyone point me in the right direction? My system is Redhat Linux 7.2, Apache 1.3.22, PHP 4.0.6. Robert@usabusiness.net