File Conversion for .doc to (.psw or .txt)

Hi,

I'm developing an PDA application of which part of it requires file
conversion from .doc to either .psw or .txt though a web service. For a
normal Windows application, I understand that this can be done in 2 ways:

1) utilising ActiveSync Filters on a PC for the conversion
2) programming a "save as" operation from a Word application from a PC

However, are any these methods possible to be implemented in a webservice?
If so, kindly advise the approach I should take, your help is greatly
appreciated..

Regards,
Missyfang