Installing PDFlib on Apache/PHP running on Windows:

I just successfully installed PDFlib on windows XP running WAMP. Here is the process:Installing PDFlib on Apache/PHP running on Windows:

Download PDFLib from:
http://www.pdflib.com/download/pdflib-family/pdflib-7/

Here is the direct download for the currently latest version for windows:
http://www.pdflib.com/binaries/PDFlib/701/PDFlib-7.0.1p1-MSWin32-php.zip

Once you have finished downloading, extract the zip file. 
In the folder "bind" choose your php version, and open that folder. (php4 or php5)

Inside that folder, you'll have PHP sub versions, choose your sub version. If you don't know the exact PHP version you'ure using, run a php page with <?php phpinfo(); ?> in it. The PHP version will be printed right at the top of the page.

Inside the sub version folder, you'll find the pdflib's .dll file for your php version.

Copy the .dll file and save the copy in your php extensions folder. This folder is defined in php.ini as "extension_dir". So if you don't know what it is on your machine, open php.ini and search for 'extension_dir'.
On my system is was: c://wamp/php/ext/

Now open php.ini and add the extension. The format for this is:

extension=file.dll

where file is the file name of the extension.

eg:

extension=libpdf_php.dll

Now you have to restart apache, and you should have pdflib installed. I tested this using:

<?php
if (class_exists('PDFlib')) {
 echo 'PDF Lib supported';
} else {
 echo 'PDF Lib not supported';
}
?>

I don't know about XAMP, you you might have the pdflib extension already added to your extensions directory. If so, then all you have to do is add the lineextension=libpdf_php.dll to php.ini