Multithreaded python script calls the COMMAND LINE

[johnny]

I have python script does ftp download in a multi threaded way. Each
thread downloads a file, close the file, calls the comman line to
convert the .doc to pdf. Command line should go ahead and convert the
file. My question is, when each thread calls the command line, does one
command line process all the request, or each thread creates a one
command line process for themselves and executes the command? For some
reason I am getting "File '1' is alread exists, Do you want to
overwrite [y/n]?" I have to manually enter 'y' or 'n' for the python
script to complete.