I have spent a lot of time on this question, namely, how to programatically use a PHP script to send a PDF document to the printer without launching the Adobe print dialog that results from using arcord32.exe (the adobe reader). PHP has some useful classes for creating PDF's, i.e., the FPDF library, but printing the created file is a bear. For Windows XP and Windows 7 servers, the one open -source solution which works is to use the PDFBOX java library. Here are the steps.
1) Download the latest java pdfbox binary: http://www.apache.org/dyn/closer.cgi/pdfbox/1.7.1/pdfbox-app-1.7.1.jar and put it in a directory. I will call my example c:/java/libs
2) Create a PDF file you want to send to the printer. I will call it example.pdf.
3) Configure the printer on the server (where PHP is running) you want to use to have a one-word name, like HPOfficeJET. You can't get away with a name like HP 8600 OfficeJet.
4) Create a command string like this:
$printcmd = "java -classpath c:/java/libs/pdfbox-app-1.7.1jar org.apache.pdfbox.PrintPDF -silentPrint -printerName HPOfficeJet example.pdf";
5) Use one of the PHP exec commands to launch this command:
If all goes well, your server's printer will start, the pdf will print, and you will have created a way to have a client page request the server to print a server PDF you select or create.