How to open some mac application on print command?

How to open some mac application on print command?

I am new to mac applications, i want to know, is there any way through
which i can open my created application whenever user tries to print a
document using a specific printer(installed by me).
i am working on conversion of .doc to .PS and then .PS to .pdf
.PS to .pdf is already achieved by me using ghost script.
The requirement of my application is to open itself whenever user tries to
print a document using a specific printer
All Suggestions are welcome, Thanx in advance