PHP calls python: process vs threads

[johnny]

What I want to do is the following:

Web user uploads a word doc, and I need it to move the uploaded word
doc, on to another machine and conver it to pdf.  Then update the
database and allow immediate pdf download.  I am thinking of using ftp
from machine 1 -> machine 2, then convert doc to pdf on machine 2,
using process or thread.  What is the best way to go about doing this,
process or threads or pyro?  Pdf is created by calling commands on the
command line, through python script.

Thank you in advance.
John